Insulating film and electronic device

ABSTRACT

An insulating film comprising: a first barrier layer;a well layer provided; and a second barrier layer is proposed. The first barrier layer consists of a material having a first bandgap and a first relative permittivity. The well layer is provided on the first. barrier layer, and consists of a material having a second bandgap smaller than the first bandgap and having a second relative permittivity larger than first relative permittivity. Discrete energy levels are formed in the well layer by a quantum effect. The second barrier layer is provided on the well layer, and consists of a material having a third bandgap larger than the second bandgap and having a third relative permittivity smaller than second relative permittivity. Alternatively, an insulating film comprising: n (n being an integer larger than 2) layers of barrier layer consisting of a material having a bandgap larger than a first bandgap and having a relative permittivity smaller than a first relative permittivity; and (n−1) layers of well layers consisting of a material having a bandgap smaller than the first bandgap and having a relative permittivity larger than the first relative permittivity, discrete energy levels being formed. in the well layer by a quantum effect, each of the barrier layers and each of the well layers being stacked by turns, and discrete energy levels being formed in each of the well layers by a quantum. effect, is provided. Alternatively, an insulating film having a lattice mismatch within a range of plus-or-minus 1.5% to the substrate, and further having a high barrier and a large permittivity is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priorityfrom U.S. Ser. No. 10/673,466, filed Sep. 30, 2003, and is based uponand claims the benefit of priority from the prior Japanese PatentApplication No. 2002-285034, filed on Sep. 30, 2002 and the priorJapanese Patent Application No. 2003-197808, filed on Jul. 16, 2003; theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an insulating film and an electronicdevice, and more particularly, it relates to an insulating film suitablyapplied to an electric field effect type transistor and ametal-insulator-metal (MIM) capacitor, and to an electronic devicehaving the insulating film. Furthermore, the present invention relatesto electronic devices, such as a MOS field effect transistor which hasthe semiconductor substrate mainly constituted by Si (silicon) and agate insulating film using the layered perovskite substance which isepitaxially grown directly on it.

In order to carry out a miniaturization of ULSI (ultra large scaleintegration) devices and to reduce power consumption, it has beendesired to make the gate insulating film thin. Conventionally, in orderto keep the amount of electric charges induced to the channel of FET(Field Effect Transistor), the technique of enlarging a capacitance hasbeen taken by making the gate insulating film thin. As the result,making SiO₂ film which is the gate oxide thin is promoted, and it isgoing to reach even the thickness below 10 angstroms (1 nm) now.

However, as long as the SiO₂ film is used, a gate leak current becomeslarge and power consumption is no longer pressed down from loss ofstandby power requirement. For example, although MOSFET operatesnormally with SiO₂ film of 8 angstroms (0.8 nm) of thickness, gate leakcurrent has reached even 1 kA/cm² and the problem in the field of powerconsumption is very big.

It is effective to increase the thickness, in order to reduce powerconsumption. For this reason, the trial to keep the amount of electriccharges by using films thicker than SiO₂ film is actively examined byemploying materials with high permittivity (high-K dielectric). However,generally as for the materials with.high permittivity, the band gaptends to become smaller. Actually, in the gate insulating film using asubstance with high permittivity like SrTiO₃, since the band offset bythe side of a conduction band becomes very small, it is difficult tostop the leak current by making the thickness quite thick. Similarsituations may take place in the case where other substances which havehigh permittivity such as (Ba, Sr, Ca) (Ti, Zr)0 ₃, Pb(Zr, Ti) O₃,SrBi₂Ta₂O₉, Ta₂O₅, CeO₂ and TiO₂ are used.

That is, band offset for silicon with these substances is very smallcompared. with 0.5 eV (an ideal is 1.0 eV or more) of a target. Thereare materials where the amount of the band offset to silicon is onlyabout 0.1 eV. The same problem exists in the case of MIM capacitors. Forexample, in a Pt/SrTiO₃/Pt capacitor, since the leak current is verylarge, it is unutilizable.

On the other hand, a laminated type insulating film using two or morelayers which consist of an insulating material is proposed (for example,Japanese Patent Laid-Open Publication No. 2000-195856, Japanese PatentLaid-Open Publication No. 2001-274393, and Applied Physics Letters 78p3292 (2001))

However, from a view point of the miniaturization for high integrationand the request of low power consumption, these laminated-typeinsulating films and the Ruddlesden-Popper type (Srn+1TinO₃n+1) filmswere not sufficient to realize both higher permittivity and lower leak.On the other hand, an invention about a perovskite type substance whichis formed on silicon substrate. with an optimized condition is proposed(Japanese Patent Laid-Open Publication No.2002-100767).

However, in the technology described in the above-mentioned JapanesePatent Laid-Open Publication No. 2002-100767, the optimum range of theperovskite type substance is sought for gate insulating films. Moreover,it is not taken into consideration about the barrier for electrons.Furthermore, it is not taken into consideration about the shift of theoptimum range at the time of introducing “distortion” into Si substrate.For this reason, the optimization in a true meaning is not carried out.In invention indicated in the Japanese Patent Laid-Open Publication No.2002-100767, the optimum range is not specified appropriately, as willbe explained in full detail later.

SUMMARY OF THE INVENITON

According to an embodiment of the invention, there is. provided aninsulating film comprising: a first barrier layer consisting of amaterial having a first bandgap and a first relative permittivity; awell layer provided on the first barrier layer, consisting of a materialhaving a second bandgap smaller than the first bandgap. and having asecond relative permittivity larger than first relative permittivity,discrete energy levels being formed in the well layer by a quantumeffect; and a second barrier layer provided on the well layer,consisting of a material having a third bandgap larger than the secondbandgap and having a third relative permittivity smaller than secondrelative permittivity.

According to other embodiment of the invention, there is provided aninsulating film comprising: a first barrier layer consisting of amaterial having a conduction band whose energy level is higher than anenergy level of a conduction band of silicon by 0.5 electron volts ormore and having a valence band whose energy level is lower than anenergy level of a valence band of silicon by 0.5 electron volts or more;a well layer provided on the first barrier layer, the well layerconsisting of a material having a bandgap smaller than a bandgap of SiO₂and having a relative permittivity larger than a relative permittivityof SiO2, and a thickness of the well layer being not larger than 10angstroms; and a second barrier layer provided on the well layer, thesecond barrier layer consisting of a material having a conduction bandwhose energy level is higher than an energy level of a conduction bandof silicon by 0.5 electron volts or more and having a valence band whoseenergy level is lower than an energy level of a valence band of siliconby 0.5 electron volts or more.

According to other embodiment of the invention, there is provided aninsulating film comprising: n (n being an integer larger than 2) layersof barrier layer consisting of a material having a bandgap larger than afirst bandgap and having a relative permittivity smaller than a firstrelative permittivity; and (n−1) layers of well layers consisting of amaterial having a bandgap smaller than the first bandgap and having arelative permittivity larger than the first relative permittivity,discrete energy levels .being formed in the well layer by a quantumeffect, each of the barrier layers and each of the well layers beingstacked by turns, and discrete energy levels being formed in each of thewell layers by a quantum effect.

According to other embodiment of the invention, there is provided aninsulating film comprising: n (n being an integer larger than 2) layersof barrier layers consisting of a material having a conduction bandwhose energy level is higher than an energy level of a conduction bandof silicon by 0.5 electron volts or more and having a valence band whoseenergy level is lower than an energy level of a valence band of siliconby 0.5 electron volts or more; and (n−1) layers of well layersconsisting of a material having a bandgap smaller than a bandgap of SiO2and having a relative permittivity larger than a relative permittivityof SiO₂, and thicknesses of the well layers being not larger than 10angstroms, each of the barrier layers and each of the well layers beingstacked by turns to form. a multi-quantum well structure.

According to other embodiment of the invention, there is provided anelectronic device capable to operate as a capacitor, comprising: a firstelectrode; an insulating film provided on the first electrode,including: n (n being an integer larger than 1) layers of barrier layerconsisting of a material having a bandgap larger than a first bandgapand having a relative permittivity smaller than a first relativepermittivity; and (n−1) layers of well layers consisting of a materialhaving a bandgap smaller than the first bandgap and having a relativepermittivity larger than the first relative permittivity, discreteenergy levels being formed in the well layer by a quantum effect, eachof the barrier layers and each of the well layers being stacked byturns, and discrete energy levels being formed in each of the welllayers by a quantum effect; and a second electrode provided on theinsulating film.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer; an insulating filmprovided on the semiconductor layer, including: n (n being an integerlarger than 1) layers of barrier layer consisting of a material having abandgap larger than a first bandgap and having a relative permittivitysmaller than a first relative permittivity; and (n−1) layers of welllayers consisting of a material having a bandgap smaller than the firstbandgap and having a relative permittivity larger than the firstrelative permittivity, discrete energy levels being formed in the welllayer by a quantum effect, each of the barrier layers and each of thewell layers being stacked by turns, and discrete energy levels beingformed in each of the well layers by a quantum effect; and a gateelectrode provided on the insulating film, an electric field in thesemiconductor layer under the insulating film being controllable byapplying a voltage to the gate electrode.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving a perovskite structure, a difference between 2^(1/2) timeslattice constant of the perovskite structure along the major plane and alattice constant of the semiconductor layer along the major plane beingnot larger than 1.5%, the perovskite structure being expressed by achemical formula ABO₃, the element A including at least one selectedfrom a group consisting of Ba, Sr, Ca and Mg, a percentage of Mg contentin the element A being not larger than 10%, the element B including atleast one selected from a group consisting of Ti, Zr and Hf, and apercentage of Ti content in the element B being not larger than 50%.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving a Ruddlesden-Popper type structure, a difference between 2^(1/2)times lattice constant of the Ruddlesden-Popper type structure along themajor plane and a lattice constant of the semiconductor layer along themajor plane being not larger than 1.5%, the Ruddlesden-Popper typestructure being expressed by a chemical formula A_(n+1)B_(n)O_(3n+1),the element A including at least one selected from a group consisting ofBa, Sr, Ca and Mg, a percentage of Mg content in the element A being notlarger than 10%, the element B including at least one selected from agroup consisting of Ti, Zr and Hf, a percentage of Ti content in theelement B being not larger than 80% in a case where n=1, a percentage ofTi content in the element B being not larger than 70% in a case wheren=2, a percentage of Ti content in the element B being not larger than60% in a case where n=3, and a percentage of Ti content in the element Bbeing not larger than 50% in a case where n≧4.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer. containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving a Ruddlesden-Popper type structure, a difference between 2^(1/2)times lattice constant of the Ruddlesden-Popper type structure along themajor plane and a lattice constant of the. semiconductor layer along themajor plane being not larger than 1.5%, the Ruddlesden-Popper typestructure having a structure where a layer expressed by a chemicalformula A2BO4 and a layer expressed by a chemical formula A₃B₂O₇ arestacked by turns, the element A including at least one selected from agroup consisting of Ba, Sr, Ca and Mg, a percentage. of Mg content inthe element A being not larger than 10%, and the element B including atleast one selected from a group consisting of Ti, Zr and Hf.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving an in-phase type structure, a difference between 2^(1/2) timeslattice constant of the in-phase type structure along the major planeand a lattice constant of the semiconductor layer along the major planebeing not larger than 1.5%, the in-phase type structure being expressedby a chemical formula A_(n+2)B_(n)O_(3n+2), the element A including atleast one selected from a group consisting of Ba, Sr, Ca and Mg, apercentage of Mg content in the element A being not larger than 10%, and

the element B including at least one selected from a group consisting ofTi, Zr and Hf.

According to other embodiment of the invention, there. is provided anelectronic device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving an in-phase type structure, a difference between 2^(1/2) timeslattice constant of the in-phase type structure along the major planeand a lattice constant of the semiconductor layer along the major planebeing not larger than 1.5%, the in-phase type structure having astructure where a layer expressed by a chemical formula A₃BO₅ and alayer expressed by a chemical formula A₄B₂O₈ are stacked by turns, theelement A including at least one selected from a group consisting of Ba,Sr, Ca and Mg, a percentage of Mg content. in the element A being notlarger than 10%, and the element B including at least one selected froma group consisting of Ti, Zr and Hf.

According to other embodiment of the invention, there is provided anelectronic device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving a well layer, a difference between 2^(1/2) times lattice constantof the dielectric film the major plane and a lattice constant of thesemiconductor layer along the major. plane being not larger than 1.5%,the well layer being expressed by a chemical formula mAO+nABO₃ (m beinginteger larger than 2, and n being integer larger than zero) where alayer of a sodium chloride structure expressed by a chemical formula AOand a layer of a perovskite structure expressed by a chemical formulaABO₃ are stacked, the element A including at least one selected from agroup consisting of Ba, Sr, Ca and Mg, a percentage of Mg content in theelement A being not larger than 10%, and the element B including atleast one selected from a group consisting of Ti, Zr and Hf.

According to other embodiment of the invention, there is provided anelectronic.device comprising: a semiconductor layer containing siliconas a major component; and a dielectric film epitaxially grown directlyon a major surface of the semiconductor layer, the dielectric filmhaving a well layer, a difference between 2^(1/2) times lattice constantof the dielectric film the major plane and a lattice constant of thesemiconductor layer along the major plane being not larger than 1.5%,the well layer having a structure where a layer expressed by a chemicalformula mAO +AB03 (m being integer larger than zero) and a layerexpressed by a chemical formula nAO+2ABO₃ (n being integer larger thanzero) are stacked by turns, including a layer of a sodium chloridestructure expressed by a chemical formula AO and a layer of a perovskitestructure expressed by. a chemical formula ABO₃, the element A includingat least one selected from a group consisting of Ba, Sr, Ca and Mg, apercentage of Mg content in the element A being not larger than 10%, andthe element B including at least one selected from a group consisting ofTi, Zr and Hf.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given here below and from the accompanying drawings of theembodiments of the invention. However, the drawings are not intended toimply limitation of the invention to a specific embodiment, but are forexplanation and understanding only.

In the drawings:

FIG. 1 is a schematic diagram showing the cross-sectional structure ofthe insulating film according to the embodiment of the presentinvention;

FIG. 2 is a schematic diagram showing the energy band diagram in theinsulating film QI of FIG. 1;

FIG. 3 is a graphical representation showing the.leak current densitywhen the voltage is applied to the insulating film;

FIG. 4 is a schematic diagram illustrating the cross-sectional structureof the insulating film which uses the double quantum well;

FIG. 5 is a schematic diagram illustrating the energy diagram of thedouble quantum well structure;

FIG. 6 is a schematic diagram showing the energy diagram in the statewhere the voltage is applied to this double quantum well structure;

FIG. 7 is a graphical representation showing the leak current densitywhen the voltage is applied to the insulating film;

FIG. 8 is a schematic diagram illustrating the cross-sectional structureof the insulating film which has the triple quantum well structure;

FIG. 9 is a schematic diagram which illustrates the energy diagram ofthe triple quantum well structure;

FIG. 10 is a sectional view of the gate insulating-film of MOSFET of thefirst example of the present invention, and CeO₂ is used for the welllayer and SrO is used for the barrier layer;

FIG. 11 is a sectional view of the gate insulating film of MOSFET of thesecond example of the present invention,. and SrTiO₃ is used for thewell layer and SrO is used for the barrier layer;

FIG. 12 is a sectional view of the gate insulating film of MOSFET of thethird example of the invention, and SrTiO₃ is used for the well layerand SrO is used for the barrier layer;

FIG. 13 is a sectional view of the gate insulating film of MOSFET of thefifth example of the invention, and SrTiO₃ is used for the well layerand SrO is used for the barrier layer;

FIG. 14 is a sectional view of the gate insulating film of MIMcapacitor, and SrTiO₃ is used for the well layer, SrO is used for thebarrier layer, and SrRuO₃ is used for the electrode;

FIG. 15 is a sectional view of the gate insulating film of MOSFET of theseventh example of the invention, and CeO₂ is used for the well layerand Ce-Silicate and SrO are used for the barrier layer;

FIG. 16 is a sectional view of the gate insulating film of MOSFET of theeighth example of the invention, and HfO2 is used for the well layer andHf-Silicate and SrO are used for the barrier layer;

FIG. 17 is a sectional view of the gate insulating film of MOSFET of theninth example of the invention, and the strained Si-SOI substrate isused, and Ca(Ti_(0.5),Zr_(0.5)) is used for the well layer and SrO isused for the barrier layer;

FIG. 18 is a sectional view of the gate insulating film of MIM capacitorof the tenth example of the invention, and (Ba_(0.2),Sr_(0.8))TiO₃ isused for the well layer and (Ba_(0.75),Sr_(0.25)) is used for thebarrier layer, and SrRuO₃ is used for the electrode;

FIG. 19 is a sectional view of the gate insulating film with the doublequantum well of MIM capacitor of the eleventh example of the invention,and (Ba_(0.2),Sr_(0.8))TiO₃ is used for the well layer and(Ba_(0.75),Sr_(0.25))O is used for the barrier layer, and SrRuO₃ is usedfor the electrode;

FIG. 20 is a sectional view of the gate insulating film of MIM capacitorof the twelfths example of the invention, and HfO₃ is used for the welllayer and Al₂O₃ is used for the barrier layer, and SrRuO₃ is used forthe electrode;

FIG. 21 is a sectional view of the gate insulating film with the doublequantum well of MIM capacitor of the thirteenth example of theinvention, and HfO₃ is used for the well layer and Al₂O₃ is used for thebarrier layer, and SrRuO₃ is used for the electrode;

FIG. 22 is a sectional view of the gate insulating film with the triplequantum well of MIM capacitor of the fourteenth example of theinvention, and HfO₃ is used for the lo well layer and Al₂O₃ is used forthe barrier layer, and SrRuO₃ is used for.the electrode;

FIG. 23 is a.graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in theperovskite type material;

FIG. 24 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in theperovskite type material when adopting Hf as B site instead of Zr ofFIG. 23.

FIG. 25 is a schematic diagram showing MOSFET which uses the insulatingfilm of this example;

FIG. 26 is a graphical representation showing relations of the.latticeconstant, the permittivity, and the band gap to the composition in RPtype material;

FIG. 27 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in RPtype material when adopting Hf as B site instead of Zr of FIG. 26;

FIG. 28 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in RPtype material in the case where it is referred to as n=2 in the materialwhose thickness of a perovskite is increased i.e., RPn, (An+1BnO₃n+1);

FIG. 29 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in RPtype material in the case where it is referred to as n=3 in the materialwhose thickness of a perovskite is increased i.e., RPn, (An+1BnO₃n+1);

FIG. 30 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in RPtype material in the case where it is referred to as n≧4 in the materialwhose thickness of a perovskite is increased i.e., RPn, (An+1BnO₃n+1);

FIG. 31 is a schematic diagram showing MOSFET which uses the RP typeinsulating film;

FIG. 32 is a graphical representation which summarizes for a gateinsulating film on a Si substrate or on a strained Si substrate surfacegrown epitaxially, and having the laminated structure (Ruddlesden-Poppertype) of the perovskite type substance ABO₃ and the layer of a sodiumchloride structure AO, where RP1 type and RP2 type are laminated byturns;

FIG. 33 is a graphical representation showing relations of the latticeconstant, the permittivity, and the barrier for electrons to thecomposition in RP type material when adopting Hf as B site instead ofZr;

FIG. 34 is a schematic diagram showing MOSFET using the insulating filmexpressed in FIGS. 32 and 33;

FIG. 35 is a graphical representation showing the gate insulating filmgrown epitaxially on a Si substrate or on a strained Si substrate, andhaving a structure where a layer of a perovskite type structure ABO₃ andtwo-layers. of a sodium chloride structure AO are laminated;

FIG. 36 is a summary of the lattice constant, the permittivity and thebarrier for electrons, etc when Hf is used for B site instead of Zr;

FIG. 37 is a schematic diagram showing MOSFET using the insulating filmexpressed in FIGS. 35 and 36;

FIG. 38 is a graphical representation showing the gate insulating filmgrown epitaxially on a Si substrate or on a strained Si substrate, andhaving a structure where IP1 type and IP2 type are laminated by turns;

FIG. 39 is a graphical representation showing relations of the latticeconstant, the permittivity, and the barrier for electrons to thecomposition in RP type material when adopting Hf as B site instead ofZr;

FIG. 40 is a schematic diagram showing MOSFET using the. insulating filmexpressed in FIGS. 35 and 36;

FIG. 41 is a sectional view of the gate insulating film of MOSFET; and

FIG. 42 is a sectional view of the gate insulating film with the doublequantum well of MOSFET.

DETAILED DESCRIPTION

Hereafter, some embodiment of the invention will be explained, referringto the drawings.

FIG. 1 is a schematic diagram showing the cross-sectional structure ofthe insulating film according to the embodiment of the presentinvention. That is, the insulating film QI of this embodiment has thequantum well structure where the well layer W is sandwiched by thebarrier layers B1and B2 from both sides.

The well layer W consists of a material which has relatively smallerband gap and relatively larger relative dielectric constant. On theother hand, the barrier layers B1 and B2 consist of materials which haverelatively larger band gap and relatively smaller relative dielectricconstant.

FIG. 2 is a schematic diagram showing the energy band diagram in theinsulating film QI of FIG. 1. Namely, the quantum levels (thequantization levels) by the. size effect are formed in the well layer Was expressed with. the broken lines in this figure, and thus, onlydiscrete energy states are allowed.

Hereafter, each layer which constitutes this insulating film QI will beexplained in detail.

First, the well layer W consists of a material which has smaller bandgap and larger permittivity compared with SiO₂. As the typical material,(Ba,Sr,Ca)TiO₃, (Ba,Sr,Ca) (Ti,Zr)O₃, Pb(Zr,Ti)O₃, Ta₂O₅, CeO₂, HfO₂,HfON, ZrO₂, ZrON, TiO₂, Hf-silicate, HfSiON, Zr-silicate, ZrSiON,Ti-silicate, other silicates or these nitrides, Y₂O₃, LaAlO₃, Ga₂O₃,La₂O₃ and Al₂O₃ can be mentioned, for example.

Next, the barrier layers Bi and B2 consist of materials which havelarger band gaps than Si (silicon). Furthermore, these layers are.desirably consist of materials whose band offset to silicon is 0.5 eV ormore on both n-side and p-side. That is, these layers are desirablyconsist of a material whose band offset is higher than silicon by 0.5 eVat a conduction band, and lower than silicon by 0.5 eV at a valenceband. Moreover, these layers are desirably consist of a material whoseband offset is higher than silicon by 1.0 eV at a conduction band, andlower than silicon by 1.0 eV at a valence band.

As the typical material, (Ba,Sr,Ca)O, SiO₂, Si₃N₄, SiON, Al₂O₃,Hf-silicate, nitride of Hf-silicate, Zr-silicate, nitride ofZr-silicate, Ti-silicate, nitride of Ti-silicate, other silicates orthese nitrides, MgAl₂O₄, (Ba,Sr,Ca)F, etc. can be mentioned.

The silicate is a candidate material for both barrier layers B1 and B2,and for the well layer W. This is because the silicate may be suitablefor both the well layer and the barrier layers by adjusting the quantityof the metal contained. Moreover, Al₂O₃ may be used for both the welllayer and the barrier layers by appropriately selecting another materiallayer to be a combined. That is, a material considered to be the type ofthe barrier layers may be adapted for the well layer, and conversely amaterial considered to be a type of the well layer may be adapted forthe barrier layers.

For example, SrO may be used for the well layer and SiO₂ may be used forthe barrier layers.

The present invention has been made in order to control effective bandoffset of a high dielectric insulating film by the quantization formedby a single well potential or a multi-well potential. Although themethod of constituting the well layer W using epitaxial growthtechnology is also leading in the present invention, since it is alsopossible to constitute the well layer by using an oriented film, apolycrystalline film or an amorphous film, the whole well layer has notnecessarily to be an epitaxial film.

In the insulating-film structure using a single quantum well, effectiveband offset can be increased to the minimum energy level (quantizedzero-point-vibration level) formed. in the well layer W.

When the electric fields applied to the insulating film are 5 MV/cm andthe SiO₂ conversion thickness i.e., equivalent oxide thickness (EOT), ofthe insulating film, is 10 angstroms, in. order to operate a computerarithmetic unit by the low power consumption not more than low, it iseffective to make leak current less than 10⁻⁵ A/cm². 0.9 eV or more ofheight of the barrier over the leak current by tunneling is required tosatisfy this requirement.

In the present invention, more efficient quantization is attained underthe following conditions and it becomes possible to raise the height ofthe tunnel barrier to 0.9 eV or more. First, the condition is to makethe. width d2 of the well layer W into 5 angstroms or less.

Moreover, the condition is that a material whose band offset for Si is 1eV or more at both n-side and p-side is used as a material of thebarrier layers B1 and B2, and that the widths d1 and d3 fulfill thefollowing conditions:

d1>2.5 angstroms; and

d3>2.5 angstroms.

Furthermore, it is more desirable to fulfill the following conditions:

d1>3.5 angstroms;

d3>3.5 angstroms;

2.5>(d1/ε1+d3/ε2); and

where ε1 and ε2 are the relative dielectric constants of the barrierlayer B1 and B2, respectively.

The condition about the width d2 of the well layer W is needed so thatthe minimum level (zero-point-vibration level) of the quantized levelamounts to 0.9 eV or more. That is, the quantization level of 0.9 eV ormore is made to form by making width d2 of the well layer W into 5angstroms or less in the present invention. Thus, the voltage at whichthe leak current which penetrates the quantum well structure byso-called “tunneling resonance” increases can be made higher than theoperation voltage of the usual electronic device. As the result, itbecomes possible to intercept the leak when applying the usual bias indevices, such. as MOSFET and MIM.

FIG. 3 is a graphical representation showing the leak current densitywhen the voltage is applied to the insulating film.

The conventional insulating film (SiO₂ insulating film) which consistsonly of SiO₂ has the characteristic that the leak current goes upexponentially to the applied voltage, as expressed by curb (a) in thisfigure.

On the other hand, in the case of the laminated type insulating filmdisclosed by the Japanese Patent Disclosures JP2000-195856A andJP2001-274393A which were mentioned above, the thickness of theinsulating layer (it corresponds to the well layer of the presentinvention) with small band gap, is 30 angstroms or more. In this case,in the operation. temperatures (in a range between −50 degreescentigrade and +100 degrees centigrade), the level in the well becomescontinuously and the quantum effects are not seen at all. For thisreason, as expressed by the curb (b) in FIG. 3, also in the case of theconventional laminated type insulating film, the characteristic of theleak current has a tendency just like SiO₂usual insulating film(thickness is the same as the equivalent oxide thickness (EOT) of thelamination insulating film), and the reduction of the leak current bythe quantum effects is not seen at all.

On the other hand, in the case of the quantum well type insulating filmof this embodiment, the quantum effects arise by making width d2 of thewell layer W into 5 angstroms or less, and the quantization level of 0.9eV or more is formed in the well layer W. As a result, since the careerdoes not penetrate the insulating film until it results in thisquantization level even if it tunnels the barrier layer B1 and B2, theleak current can be decreased sharply. And if applied voltage is furtherenlarged to a quantum well type insulating film, as expressed by thecurb (c) in FIG. 3, the leak current will raise in peak. This expressesthe state where the career penetrates the whole insulating film throughthe quantization level formed in the well layer W by tunnelingResonance.

The quantization level obtained by making width d2 of the well layer Winto 5 angstroms or less is higher than the voltage range of operationof the usual MOSFET or MIM. For this reason, as expressed in FIG. 3, theleak current can be reduced in the whole voltage range of operation.

Next, if the widths dl, d3 of the barrier layers B1, B2 are too thin,the effective barrier height decreases. And the quantum levels spreadout from the well by a quantum tunneling. By making the width of thebarrier layers B1 and B2 3.5 angstrom or more, these problems will beavoided nearly completely, but even if it is 2.5 angstroms, the effectsof about a half can be acquired. Therefore, 3.5 angstroms or more isdesirable, but if 2.5 angstroms, the minimum quantum effects will beattained. That is, the barrier layer B1 and B2 need the barrier widthsof 2.5 angstroms or more. And the barrier widths of 3.5 angstroms ormore is more desirable.

If the barrier layer B1 and B2 are too thick, the equivalent oxidethickness (EOT) will exceed 10 angstroms. In order to prevent thisproblem, the width d1 and d3 of the barrier layer B1and the barrierlayer B2 and the relative dielectric constants ε1 and ε2 must at leastsatisfy the following condition:

2.5>(d1/ε1+d3/ε2)

When the electric field applied to the insulating film is 5 MV/cm andthe equivalent oxide thickness (EOT) of the insulating film is 10angstroms, a computer arithmetic unit may be operated at a powerconsumption of 100 watts. In this case, it is effective to suppress theleak current less than. 10⁻² A/cm². This may be realized if there is0.25 eV or more of barrier height to the leak current by tunnel. And inorder to realize this situation by employing a quantum well structure,the barrier height is to be made higher than 0.5 eV and the well widthis to. be made 10 angstroms or less. These conditions are quite easy tosatisfy, and thus, the range of choice of materials can be spreadgreatly.

Next, the insulating film using double quantum well structure will beexplained.

FIG. 4 is a schematic diagram illustrating the insulating film whichuses the double quantum well. That is, this insulating film is thestructure where the well layers. W1 and W2 are inserted into.barrierlayers B1 through B3. The well layers W1 and W2 consist of materialswhich have relatively small band gaps and relatively large dielectricconstants. On the other hand, the barrier layers B1 through B3 consistof materials which have relatively large band gaps and whose relativelysmall dielectric constants.

FIG. 5 is a schematic diagram illustrating the energy diagram of thedouble quantum well structure.

In the insulating-film structure using the double quantum well, bychanging the width of the first well layer W1 and the width of thesecond well layer W2, it becomes possible to shift greatly the energylevel (illustrated with the broken line of the quantum level formed ineach well layer as illustrated in FIG. 5. In this case, it becomespossible to make effective band offset into the height of the barrierlayer directly by shifting the energy level made in the inside of bothof the well layers W1 and W2. Consequently, it becomes possible to makea very high energy barrier.

FIG. 6 is a schematic diagram showing the energy diagram in the statewhere the voltage is applied to this double quantum well structure.

Thus, since the potential of each well layer will change if the voltageis applied, the energy level may approach or may be agreement withadjacent well layers.

For example, in the case of the example of FIG. 6, the minimum level (itcorresponds to the broken line of the bottom in W1) of the well layer W1and the 2 ^(nd) level (it corresponds to the broken line of the top inW2) of the well layer W2 have almost same level.

Since the band offset falls rapid1y in such a condition, it 16 isdesirable that the difference of the energy level of both of well layersis large.

However, if it laminates so that the well layer of the one where wellwidth is thinner may be located in the high potential side when width d2of the well layer (it is the well layer W1 in FIGS. 5 and 6) of the onewhere well width is thinner is made into 5 angstroms or less and voltageis applied even if the energy level. between adjoining well layers is inagreement, it will become possible to make an about 1 eV barrier.

According to this embodiment, it becomes possible to raise the heighteffective band offset) of the tunnel barrier from 1.5 eV to 3 eV or more(value corresponding to band offset of the barrier layer). It is idealthat the energy difference of the energy level made in two well layersis large enough and it becomes larger than the maximum (which is assumedto be about 0.4 eV) of the “deviation” caused by the voltage applicationat the time of the operation of the semiconductor device using thisinsulating film by ten percent or more (which is assumed to be about0.04 eV). Since “deviation” of the energy caused by a voltageapplication is greatly dependent on the width d3 of barrier layer B2.And the required applied voltage depends on the permittivity of thewhole film. Therefore, it is quite possible to prevent theinter-coupling of the levels of neighboring well layers below theoperating voltage by controlling the thicknesses of the wells andbarriers.

FIG. 7 is a graphical representation showing the leak current densitywhen the voltage is applied to the insulating film.

Detailed explanation will be omitted about the same elements as what wasmentioned above with reference to FIG. 3. It becomes possible todecrease the leak current further by making it double quantum wellstructure.

The peak-rise of the leak current can also be suppressed certainly bypreventing the coincidence of the quantization level between the quantumwell W1 and W2, as expressed by the curb (d) in FIG. 7.

On the other hand, about the width d1, d3, and d5 of the barrier layersB1 through B3 used here, it is desirable to fulfill the followingconditions.

d1>2.5 angstroms;

d3>2.5 angstroms; nd

d5>2.5 angstroms.

Furthermore, it is more desirable to fulfill the following conditions.

d1>3.5 angstroms;

d3>3.5 angstroms;

d5>3.5 angstroms; and

2.5>(d1/ε1+d3/ε2+d5/ε3).

Here, ε1,ε2, and ε3 are the relative dielectric constant of the barrierlayer B1, B2, and B3, respectively.

The conditions about the width of these barrier layers are given fromthe same view as the conditions about the single type quantum wellstructure which was illustrated in FIGS. 1 and 2.

On the other hand, it is also possible to shift the energy level insideof the well layers by changing the material of the well layer W1 and thematerial of W2 in double quantum well structure. Moreover, the materialsused for the barrier layers B1-B3 does not need be identical. That is,each of the barrier layers B1-B3 may be made of different material. Thematerials for the barrier layers may be appropriately selectedconsidering the structure of the device, condition of the formationprocess, etc.

In the insulating-film structure using double quantum well structure, itis also possible to change the way of thinking, and to design structure.That is, when voltage is not applied, the energy levels of the two welllayers W1 and W2 need not to deviate largely. These energy levels can bemade to deviate when the voltage is applied. In this case, when thevoltage is not applied, the energy levels of two well layers mayapproach, or may become the same.

For example, when the widths of two well layers are the same, the energylevels of two well layers become the same. In the case that the welllayer is constituted like the single quantum well structure (it isdesirable that the width d2 and d4 of each well layer W1 and W2 is 5A orless), when the voltage is not applied, the barrier is only 1 eV orless, but when the voltage is applied, an effective barrier becomeshigh. In this case, if there are plurality of energy levels in the welllayer, it is possible to design so that the differences between energylevels in a well become larger than 1.5 eV.

Then when the insulating film of the invention is applied tosemiconductor devices, such as MIM, even if the bias voltage is applied,coincidence of the energy level between well layers is not generated.

And since the thickness required to constitute a well layer can be madesmall, it is especially effective to enlarge the capacitance. However,the barrier layer B2 with a width of 3.5 angstroms or more is requiredbetween the well layers. W1 and W2 so that an interaction may not workbetween them, in this case.

When width d3 of the barrier layer B2 is made small, a spread appears inan energy level. Consequently, even when the voltage is applied, sincethe height of the effective barrier falls to about 0.7 eV the energy dueto the coupling of energy levels of the neighboring well layers, highperformance can not be expected.

Also in the multi quantum well structure provided the three ormore-layer quantum well layer, the same thing can be said as mentionedlater. In the case of a three or more-layer quantum well layer, if thewidth of the barrier layer is smaller than 2.5 angstroms, it isnecessary to design the quantum well structure taking consideration thatthe more the well layer is piled up, the more a spread of a levelbecomes large.

In the case of the insulating film of the present invention, to make thethickness between quantum wells of the barrier layer into 3.5 angstromsor more in multi quantum well structure is important.

If the thickness of the barrier layer becomes small, the width of thequantum level of the well layer spreads as mentioned above, aconfinement of electrons will become weak and it will be advantageousfrom a viewpoint of a kinetic energy. However, in the invention, even ifthere is an energy loss of the kinetic energy, it is necessary to designso that there may be no interaction between the energy levels as much aspossible.

On the other hand, in the report (Applied Physics Letters 78 p3292(2001)) mentioned above, a discussion about the method of the epitaxialgrowth on the SrTiO₃ substrate of Srn+1TinO3n+1 is disclosed.Srn+1TinO₃n+1 is a Ruddlesden-Popper (RP) type material.

“Srn+1TinO₃n+1 can be used. as a gate insulating film of MOSFET” isindicated in the text. However, Srn+1TinO3n+1 which is one of RP typematerial does not form the quantum well structure needed by theinvention.

Srn+1TinO3n+1 does not function as an insulating film adapting multiquantum well structure from which the height of an effective barrierturns into height of the barrier of a barrier substance. This is becausethe thickness of the region corresponding to the barrier is very thin,and the quantum level is not formed since the band (it corresponds tothe continued energy) which spread in the direction of the thickness.

Therefore, the insulating film with a big barrier using well structurecannot be formed, but “the insulating film whose effective barrierheight corresponds with the barrier height of a barrier substanceobtained by the invention” is a completely different insulating film.

In the invention, quantization of the energy levels (discrete levelformation by quantum effect) in accordance with a design policy which isexplained in full detail below is indispensable conditions. Unless thequantization takes place, it is impossible to realize “the insulatingfilm whose effective barrier height corresponds with the barrier heightof a barrier substance.”

In order to make the quantum well structure as explained in thespecification, one of the following design methods may be performed.Both of the design methods intercept completely the interaction in thedirection of the thickness of the substances (well partial structurematerial) which occupy internal Ti site. The 1st design method is“designing the super-lattice structure modulation having been added tothe thickness of the well layer so that a discrete resonance quantumlevel's may occur (for example, 3.9 angstroms and 7.8 angstroms beingprovided by turns as thickness of the well layer.).” The 2nd designmethod is “designing the barrier layer thickly enough so that a discreteresonance quantum level's may occur (there being only about 2.5angstroms at RP type, although it is at least 3.5 angstroms).”

RP type substance disclosed in the report (Applied Physics Letters 78p3292 (2001)) is applied to this neither, and cannot raise greatly thebarrier for electrons and the electron hole barrier in operationtemperature.

In the invention, the reason it is important that a discrete resonancequantum level occurs is that it means that the electron (or hole) isconfined in the inside of a well. That is, it is because that when itsees from the outside it is visible as if effective mass is largeinfinitely.

That is, since the effective mass of the direction of the thickness ofthe electron which enters inside of the well resonating becomes verylarge, it is visible as if the mobility. of the direction of thethickness became substantially zero. In the insulating film adapting thequantum well according to the design of the invention, effective barrierheight is in agreement with the barrier height of a barrier substance.Therefore, it becomes possible not only to have a very big barrier forelectrons and a hole barrier, but also to reduce the penetrationprobability of the insulating film more nearly extraordinarily than thepenetration probability of the electron (or hole) included in the usualband.

In the conduction band in which the band is formed, this effect is notapplied at all. Therefore, by RP type substance which is indicated bythe report (Applied Physics Letters 78 p3292 (2001)), since penetrationprobability will still be large even if the barriers for electronsbecome large for about 0.8 eV, the leak current cannot fully bedecreased like the case of the insulating film adapting a quantum well.

As the result, when compared by the EOT (equivalent oxide thickness) thethickness converted into SiO₂ thickness), in RP type of the report(Applied Physics Letters 78 p3292 (2001)), the reduction of the leakcurrent is smaller than the insulating film of the invention. By theinsulating film of the invention, the decrease of about 10⁻⁸ times ofthe leak current is expectable compared with the same SiON film of EOTto explain in full detail as an example later.

On the other hand, in the RP type substance indicated by the report(Applied Physics Letters 78 p3292 (2001)), it turned out in anexperiment that the leak current falls only about 0.1 times comparedwith a SiON film.

In the integrated circuit for today's computer arithmetic units, it iscalled for that the power consumption of an operation chip is less thanat least 100 W. It is a realistic target by considering the operationperformance as important, to keep the power consumption 100 W or less,when the power consumption is in a midd1e range, and to keep it 10 W orless, when the power consumption is kept as small as possible.

Of course, getting worse is not realistic although it is good for powerconsumption to decrease further rather than this. What is necessary isjust to consider a realistic maximum value in the meaning.

Respectively, in the case of holding down power consumption to 100 W and10 W, when the electric fields are 5 MV/cm and the equivalent oxidethickness (EOT) of an insulating film is 10 angstroms, it is effectiveto hold down leak current to less than 10⁻² A/cm² and 10⁻⁵ A/cm2respectively. And since the amount of leak current is greatly dependenton the barrier over an electron and a hole, it can be estimated thebarrier needed over electron and hole.

About a hole, a barrier which exceeds 1 eV is reported in manysubstances, and since all the substances included by the invention areover 1 eV, they do not become a problem.

In a well type, 0.25 eV and 0.9 eV are required respectively for thebarrier over an electron. When an electron goes into a band like the RPtype structure or the perovskite structure, 0.85 eV and 1.0 eV areminimum requirement for the barrier height to an electron.

In order that an electron may go into a band, an improvement is notenough, electric fields are 5 MV/cm, and although a barrier forelectrons is about 0.8 eV in RP1 type Sr₂TiO₄, when the equivalent oxidethickness (EOT) of an insulating film is 10 angstroms, leak current isactually less 10⁻¹ A/cm². If compared with. SiO₂, it will be theimprovement of triple figures, but it becomes a value also with thepower consumption near [it is inadequate and] 200 W. The state of sayingthat operation performance is also high (mobility is very large) is theoptimum at power consumption 10 W or less. Therefore, it is desirablefor a barrier for electrons to be 1.0 eV or more in the perovskitestructure and RP type by which an electron goes into a band. Moreover,when Si substrate is used, it is desirable for mobility to be more than400 cm²/Vsec.

In MOS structure, the mobility has relation in the interface electriccharge trap density Dit (cm⁻²/eV) directly, and Dit depends to thelattice constant difference between a substrate and an insulating filmstrongly in epitaxial growth. And although Dit is very small andmobility is very large at 1.5% or less, Dit increases rapid1y in thestage exceeding 1.5%, and mobility decreases rapid1y. At 1.5% or less,mobility is more than 400 cm²/Vsec to Si substrate, and Dit is less than8×10¹¹cm⁻²/eV.

Moreover, also in a strained Si substrate, although the value of theoptimum mobility and Dit change depending on the amount of distortion,it is the same as that in a Si substrate. That is, if it is 1.5% or lessof lattice constant difference, Dit is very small, and mobility is alsovery large, but if it exceeds 1.5%, Dit will increase rapidly andmobility will decrease rapidly.

When the perovskite structure and the RP type substance with which anelectron goes into a band are used so that the above explanation mayshow, in order to reduce power consumption, securing the working speedof MOSFET, it is required for a barrier for electrons to be 1.0 eV ormore, and for a lattice constant difference between a substrate and aninsulating film to be less than 1.5%. Moreover, since change of themobility in well type insulating film by the difference of a latticeconstant is completely the same the difference of less than 1.5% oflattice constant serves as a boundary line of the optimum range.

Next, the insulating-film structure of having triple quantum wellstructure will be explained.

FIG. 8 is a schematic diagram illustrating the cross-sectional structureof the insulating film which has the triple quantum well structure. Thatis, the first through third well layers W1, W2 and W3 have the structureinserted into the first through the fourth barrier layer B1 through B4.The well layers W1through W3 consist of materials which have relativelysmall band gaps and relatively large relative dielectric. On the otherhand, barrier layers B1 through B4 consist of materials which haverelatively large band gaps and relatively small relative dielectric.

FIG. 9 is a schematic diagram which illustrates the energy diagram ofthe triple quantum well structure.

In the triple quantum well structure illustrated in FIGS. 8 and 9, thewidth d2 of the first well layer W1 and d6 of the third well layer W3 isthe same, and the width d4 of the second well layer W2 differs from thatof the first and the third well width. Then, the fall of the band offsetby a quantization energy level being in agreement among all quantum welllayers when the voltage is applied can be prevented.

That is, when the voltage is applied and the levels of the first welllayer W1 and the second well layer W2 are in agreement, the level ofthird well layer W3 differs from these levels.

The energy level of well layers can be adjusted by setting up the widthand material of wells and, the thickness and material of barrier layersappropriately.

Here, the typical materials which constitute a well layer and a barrierlayer are the same as those of what was mentioned above.

In the invention,. it becomes possible to raise the height of the tunnelbarrier of the insulating film to 1.5 eV-3.0 eV more.

When voltage is applied, the height of a tunnel barrier can be raised bymaking the energy levels made in first through third well layers W1through W3 not in agreement as illustrated in FIG. 6.

For example, the width d2 and d6 of the first and the third well layersare the same and are 5 angstroms or less, and the width d4 of the secondwell layer W2 is more than 5 angstroms and less than 10 angstroms, theheight of a tunnel barrier can be raised.

About the thickness of the barrier layer, the same conditions as theformer are required.

Namely,

d1>2.5 angstroms;

d3>2.5 angstroms;

d5>2.5 angstroms; and

d7>2.5 angstroms.

Furthermore, it is more desirable to fulfill the following conditions.

d1>3.5 angstroms;

d3>3.5 angstroms;

d5>3.5 angstroms;

d7>3.5 angstroms; and

2.5>47 (d1/ε1+d3/ε2+d5/ε3+d7/ε4).

Here, ε1, ε2, ε3, and ε4 are the relative dielectric constant of thebarrier layer B1, B2, B3 and B4, respectively.

It is possible to change the energy levels made in well layers by usingmaterials which are different in the well layers W1, W2 and W3 like thecase of a double well.

Moreover, it is not necessary to use the material as all barrier layerswith the same material used for barrier layer B1 through B4 as well asthe case of a double well.

As mentioned above, the quantum well structure application insulatingfilm using a quantization level (discrete level by quantum effects) wasexplained in full detail.

Next, especially the optimum substance as a gate insulating film at thetime of making it grow epitaxially directly on Si (or on a strained Si)about the “perovskite type substance ABO₃” and “the lamination structureof the perovskite type substance ABO₃ and the rocksalt type substanceAO” is explained irrespective of the existence of adaptation of quantumwell structure. Here, A is at least one of Ba, Sr, calcium, and the Mg,and B is at least one of Ti, Zr, and the Hf(s).

First, the conditions of the gate insulating film on Si (or on strainedSi) are the following three points. As far as the inventors gets toknow, before the invention, the material which fulfills simultaneouslythe following “indispensable 3 conditions as an insulating film” was notfound out.

(1) In order to make the interface characteristic well and to keep themobility of both electron and hole high, you have to hold down thelattice constant of an insulating film plus-or-minus 1.5% to the latticeconstant of a substrate at the maximum, taking the rotation of a crystalaxis into consideration. (when making it grow. up to be Si (001)surface, a crystal axis rotates 45 degrees and it grows) (when there is1.5% or more of lattice constant difference, the interface electriccharge increased rapidly and the mobility decreased suddenly.) Thelattice constant of the substrate of Si substrate in which distortion isnot contained is 5.43 angstroms. Therefore, the lattice constant of theinsulating film multiplied by √2 (45-degree rotation) must be in therange of 5.349 angstroms to 5.511 angstroms.

For example, since the lattice constant of the substrate of the siliconsubstrate containing distortion of plus 1% is 5.484 angstroms, thelattice constant of an insulating film must be more than 5.402 angstromsand less than 5.567 angstroms. Since it is thought that a strained Sisubstrate etc. will come to be used frequently from now on, it isrequired to choose a lattice constant, taking the amount of distortionof a substrate into consideration.

In the present invention, after considering the case where perovskitetype substance ABO₃ thin film grows epitaxially directly on Si (001)substrate and where the thin film of Substance AO (A is set to at leastone of Ba, Sr, calcium, and the Mg) rocksalt structured and perovskitetype substance ABO₃ thin film grow epitaxially by turns, the optimumsubstance in the range of this structure is chosen.

A lattice constant is controllable by both the substitution (A and B) ofstructure material, and the number of sheets of AO thin film to beinserted.

Hereafter, as a concrete example, although the amount of distortion of astrained Si substrate is set to plus 1%, it is clear that a regionshifts with the amount of distortion. That is, in the followingexplanation, as an example of representation, plus 1% of case is onlyshown, and you may not necessarily be plus 1%. By strained SOI (siliconon insulator) etc., since the realizable amount of distortion is aboutplus 1% in the present stage easily, plus 1% is actually made into theexample of representation, but it is thought that creation of thestrained Si substrate which reaches to 2% or more is attained easily inthe future.

For example, if the amount of distortion of a strained Si substrate isplus 1.5%, the lattice constant of a strained Si substrate will become5.511 angstroms. Therefore, a thin film with a lattice constant of 5.428to 5.594 angstroms needs to be formed as a film. If the amount ofdistortion of the strained Si substrate is plus 2%, the lattice constantof the strained Si substrate will become 5.539 angstroms. Therefore,gate insulating thin film with 5.456 to 5.622 angstroms lattice constantneeds to be formed as a film.

Moreover, when the lattice constant by the side of the substrate mayhave comes to be operated freely, it becomes possible to control thelattice constant of the strained Si substrate so that it is suited forthe lattice constant of a gate.insulating film. However, since itslarger possible one is good when the amount of distortion of a strainedSi substrate is taken into consideration from the relation of themobility, it is as much as possible desirable [enlarging distortion of astrained Si substrate] to unite the lattice constant of a gate.insulating film with it as much as possible.

And even when the lattice constant. of a strained Si substrate is plus2% as explained as an example later (5.539 angstroms of latticeconstants), it is possible to optimize the gate insulating film.

Here, the lattice constant is 5.93 angstroms when the lattice constantof the substance BaZrO3 of the invention is multiplied by 2^(1/2).Therefore, the full limits (larger 1.5% than it) of the lattice constantof the strained Si substrate become 6.02 angstroms. In this marginalcondition, since the amount of distortion of a strained Si substrate hasreached to 11%, it is thought that it is over the limit of the amount ofdistortion which can be introduced into a silicon substrate inelasticity. That is, if the gate. insulating film of the invention isused, all the distortion substrates that have the realistic amount ofdistortion can be covered.

(2) It is needed that the barrier is sufficiently high. As mentionedabove, a barrier to a hole at a “perovskite type substance” and “thelamination structure of a perovskite type substance and the substance ofrocksalt structure” of the invention is large enough (about 2.0 eV iskept). Then, it is necessary to search for the conditions that thebarrier for electrons is 1 eV or more. Although this condition is veryexacting, if it designs based on the invention, it will become possiblein the very large condition range. When using the quantum wellinsulating film using a discrete resonance quantization levelespecially, since the barrier height (about 2.5 eV is expectable withthe rocksalt structure considered here.) of a barrier substance is alsoreached, it can realize easily.

(3) As a relative dielectric constant, to fill (real thickness(angstrom))/(relative dielectric constant)<2.5 (angstroms) is needed.

If this condition is fulfilled, equivalent oxide thickness (EOT) willbecome 10 angstroms or less, and a required electric charge will bekept. Here, since the real thickness is more effective as it is thick,it is desired for permittivity to be large as much as possible.

At least 20 or more are required for the relative dielectric constant ofthe usual thin film.

On the other hand, as mentioned above, since it uses a non-resonancestate in using the quantum well insulating film using a discretequantization level, the tunnel probability becomes extremely small.

In this case, even if the thickness is thin, it becomes possible to keepthe leak current extremely small. Therefore, even if the thin film thatthe whole relative dielectric constant becomes small is used, it becomespossible to keep the leak current small. This point is one of theessential effects acquired for the first time by using the quantum wellinsulating film using the discrete quantization level. As the result, italso becomes possible to lower the minimum of the relative dielectricconstant to. about ten.

Two methods can be considered in order to constitute the thin film whichsatisfies all of three conditions explained above. The first method is amethod of using the quantum well insulating film using a discretequantization level as mentioned above. Moreover, the second method is amethod of optimizing the substance itself. Moreover, it becomes possibleto expand the range of an effective substance by combining the first andthe second method.

Hereafter, the second method is explained in detail. Here, the“perovskite type substance ABO₃” and “the lamination structure of theperovskite type substance ABO₃ and the substance AO of rocksaltstructure” are mentioned as an example, and it explains that they can besatisfy all of the three above-mentioned conditions (1) lattice constant(2) barrier for electrons (3) permittivity. Moreover, all thecalculation results were sampled appropriately and checked by the actualtrial production experiment.

First, a barrier for electrons is explained. By the perovskite typesubstance ABO₃, even if A site changes to Ba, Sr, Ca, and Mg, the bandgap and the barrier for electrons hardly change. On the other hand, whenB site is changed, it became clear that the barrier for electronschanged a lot. And it became clear that it is possible to increase thebarrier for electrons to 1 eV when forming the perovskite type substanceABO₃ as a film directly on Si, by filling (amount of Ti)/ amount ofTi+amount of Zr+amount of Hf<=0.5.

Below, the optimum regions are explained for every structure.

(1) The case of “the perovskite type substance ABO₃” which is anepitaxial growth on a Si substrate or a strained Si substrate.

FIG. 23 is a graphical representation showing relations of the latticeconstant, the permittivity, and the band gap to the composition in theperovskite type material. The horizontal axis of this figure correspondsto the composition of A site atom in a chemical formula ABO₃, and avertical axis corresponds to the composition of B site atom. Here, inthe chemical formula ABO₃, the lattice constant, the permittivity, andthe band gap at. the time of choosing A=(Ba, Sr, Ca, Mg) or B=(Ti, Zr),respectively are expressed concretely. Moreover, the 5.43 angstromscontour line S1 which is the lattice constant of Si substrate is alsoexpressed. Moreover, the 5.511 angstroms contour line S2 which is themaximum (plus 1.5%) of the lattice constant is also expressed with thesolid line. Furthermore, the 5.349 angstroms contour line S5 which isthe minimum (minus 1.5%) of the lattice constant is also expressed withthe solid line.

That the lattice constant of the insulating film is between a contourline S2 and a contour line S5 is the conditions U adjusted in a siliconsubstrate. The region which is suited for conditions U and whose barrierfor electrons is 1.0 eV or more will be described as a region “A” afterthis.

The barrier for electrons will be set to 1 eV or more if the rate of Zrwhich occupies B site is made into 50% or more. Therefore, in the graphof FIG. 23, the range of a lower half expressed with the slash agrees onthe conditions that a barrier for electrons is high (1 eV or more). Ascompared with the permittivity of each material, it turns out that thepermittivity of a perovskite type substance is sufficiently large.However, if there is much Mg, it becomes impossible to form a perovskitetype substance, and permittivity will fall. Therefore, it is necessaryto adjust the rate of Mg so that the lattice constant may be made smallmaking it to 10% or less.

The above consideration shows that the region which fills the above“indispensable 3 conditions as the insulating film” does not exist aboutepitaxial growth on Si substrate. In the Japanese Patent DisclosureJP2002-100767A mentioned above, it is considered that the region X shownin FIG. 23 is the optimum region. However, the “deviation” from theconditions U or a small barrier for electrons less than 1 eV can saythat Region X is not suitable as a gate insulating film.

On the other hand, since the optimum lattice constant in the epitaxialgrowth on an about plus 1% strained Si substrate becomes large, therange to adjust is caught. That is, the lattice constant of a strainedSi substrate with distortion of plus 1% is 5.484 angstroms, and thecontour line S3 is as illustrated. The maximum of the lattice constantof the gate insulating film adjusted in this lattice constant is 5.56angstroms, and is expressed by the contour line S4.

Moreover, the minimum of the lattice constant is 5.40 angstroms and isexpressed by the contour line S6. That the lattice constant of aninsulating film is between the contour line S4 and the contour line S6are the conditions V adjusted in a strained silicon substrate withdistortion of about plus 1%. The region which is between contour linesS4 and S6 (suiting Conditions V) and whose barrier for electrons is 1 eVor more (slash hatch part) is the region B expressed in this figure. Forexample, in the case of Ca(Ti_(0.4),Zr_(0.6))O₃, a barrier for electronsis about 1.2 eV, a lattice constant is 5.556 angstroms, and permittivityis about 40, and it is able to create a very ideal thin film.

In the Japanese Patent Disclosure JP2002-100767A, reference is madeabout strained Si as an example 4. However, in the example 4 of theJapanese Patent Disclosure JP2002-100767A, (Sr_(0.5),Ca_(0.5))TiO₃ whichhardly produces a barrier for electrons is used. That is, in thisreference, it is not taken into consideration about a barrier forelectrons. The Japanese Patent Disclosure JP2002-100767A is describingthe region R1 in FIG. 4 thereof as a range which the lattice constantadjusts. However, this corresponds to the solid line S1 which shows 5.43angstroms of lattice constants of Si in FIG. 23 of the text, and theoptimum region does not exist on this straight line.

Moreover, it is clear that the optimum range shifts with the amount ofdistortion of a strained Si substrate. For example, if the amount of thedistortion is plus 1.5%, the lattice constant of a strained Si substratewill become 5.511 angstroms. Therefore, it becomes necessary to form athin film with 5.428 to 5.594 angstroms of lattice constant as a film.That is, the optimum range becomes larger than Region B. Since therelation of the amount of distortion and the optimum range is the samein each example explained later, detailed explanation is omitted in thefollowing examples.

FIG. 24 is a graphical representation which summarized the latticeconstant, the permittivity, the band gap, etc. when adopting Hf as Bsite instead of Zr.

Also in this figure, the contour lines S1-S6 of the same latticeconstant as FIG. 23 were expressed.

As compared with the case of Zr, the lattice constant of Hf is smallerthan that of Zr about 0.6%. When Hf is used compared with the case whereZr is used, the optimum region shifts somewhat, but there is noessential change.

As explained above, it turned out that a good insulating film can beformed when a strained Si substrate. is used, although it is difficultto form the optimum insulating film on Si substrate on the substance ofa perovskite structure explained about FIGS. 23 and 24.

FIG. 25 is a schematic diagram showing MOSFET which uses the insulatingfilm of this example.

That is, the source region S and the drain region D are formed on thesurface of a silicon substrate or the strained silicon substrate 151.And the insulating film 152 mentioned above is provided on the channelregion between these source region and drain region, and the gateelectrode 153 is provided. on the insulating film 152. And MOSFET ofhigh speed and low power consumption is realizable by using the materialin the range of Region B expressed in FIG. 23 and FIG. 24 as a materialof the-gate insulating film 152.

Next,. FIG. 26 is a graphical representation showing an example whenusing RP type material. A lattice constant, permittivity, a band gap,etc. of a case (it abbreviates to “RP1 type”.) of n=1 were summarized inRP type A_(n+1)B_(n)O_(3n+1) in this figure. That is, this figure isconcern about epitaxial growth to Si substrate or a strained Sisubstrate, and is a graphical representation which summarized a latticeconstant, a band gap, permittivity, etc. about the material which hasthe structure where the perovskite type substance ABO₃ and the nature AOmono layer of a brocksalt structure were made to laminate by turns.Moreover, also in FIG. 26, the contour lines S1-S6 of a lattice constantare expressed like FIG. 23. Moreover, also in FIG. 26, (Ba, Sr, Ca, Mg)are mentioned as an atom which occupies A site and (Ti, Zr) arementioned as an atom which occupies B site, respectively.

First, by RP type substance, if a band gap is explained, as mentionedabove, since the barrier portion is too thin, the quantum wellinsulating film in which a discrete quantization level is formed cannotbe obtained.

Therefore, it is necessary to increase the amount of Zr(s) (or Hf) andto raise the barrier for electrons (ΔEc) to 1 eV or more. By. RP1 typesubstance, when the percentage of Zr (+Hf) is 20% or more, the barrierfor electrons is 1 eV or more. Therefore, if it is in the shadow area ofFIG. 26, it turns out that the conditions that. a barrier for electronsis 1.0 eV or more are fulfilled. On the other hand, about permittivityepsilon, when Ba, Sr, and Ca are used for A site, 20 or more areobtained in all the ranges. However, when Mg contains to A site, ifthere are many amounts of Mg, it will become impossible to form aperovskite type substance, and permittivity will fall. Therefore, arange in which the rate of Mg is made being less than 10% and thelattice constant is made small making the amount of Zr increase isoptimum.

Next, a lattice constant will be explained. Also in FIG. 26, the contourline S1 of 5.43 angstroms of lattice constants of Si substrate and the5.511 angstroms contour line S2 which is a maximum over the latticeconstant were expressed, respectively.

As a result of the above consideration, in the non-strained Si, therange which fulfills the above-mentioned “indispensable 3 conditions asan insulating film” is the region A in FIG. 26. In this region, in thesubstance which exists down the figure, a barrier for electrons becomeshigh. Therefore, if it is the thin film of a substance which mixed asmall amount of Mg, making the amount of Zr(s) increase to Ca₂(Ti_(0.5),Zr_(0.5))O₄ or here, it can be said that the powerful thin film as aninsulating film is obtained.

In the report (Haeni, Appl. Phys. Lett. 78 p.3292 (2001)) mentionedabove, the possibility as a gate insulating film of Sr₂TiO₄ expressed inFIG. 26 is suggested. However, as shown in FIG. 26, since the barrierfor electrons of Sr₂TiO₄ is not high enough, the leak current cannotfully be reduced.

Moreover, since the optimum lattice constant in the epitaxial growth onan about plus 1% strained Si substrate becomes large, the optimum rangeis spread. The lattice constant of the strain Si with strain of plus 1%is 5.484 angstroms, and is expressed by the contour line S3. Moreover,5.56 angstroms of lattice constants adjusted to this lattice constant isexpressed by the contour line S4.

Therefore, the region which suits to the strained Si of plus 1% isRegion A and Region B in FIG. 26. This shows that the substance of thevery large range functions as a gate insulating film to strained Si. Forexample, if it is Ca₂(Ti_(0.4),Zr_(0.6))O₄, the very ideal thin filmwhose barrier for electrons is about 1.8 eV, lattice constant is 5.526angstroms, and permittivity is about 30 can be created.

FIG. 27 is a graphical representation which summarized the latticeconstant, the permittivity, and the band gap when adopting Hf as B siteinstead of Zr of FIG. 26. Also in this figure, the contour lines S1-S6of the same lattice constant as FIG. 23 were expressed.

When Zr is compared with Hf, the lattice constant at the time of usingHf is smaller than that of Zr about 0.6%. That is, when Hf is usedcompared with the case of only Zr, an optimum region shifts somewhat,but there is no essential change. That is, Region A suits as a gateinsulating film to the Si, and Region A and Region B suit to the strainSi of plus 1%.

Moreover, only since an optimum region will only shift somewhat if thecase where Zr is used is compared with the case where Hf is used, as anatom of B site, explanation when Hf replaces is omitted in the followingexplanation.

Next, in the substance in which the thickness of a perovskite structureregion is increased, i.e., RPn, (An+1BnO₃n+1), the case where it isreferred to as n=2, n=3, and n≧4 is summarized into FIG. 28, FIG. 29,and FIG. 30, respectively. Moreover, also in these graph, the contourlines S1-S6 of a lattice constant were expressed.

In any case, permittivity epsilon is large enough, but in order to keepa barrier for. electrons (1 eV or more), it is needed that a ratio of(Zr+Hf) of B site are 30% or more, 40% or more, and 50% or more,respectively. And the first-principles calculation and an experimentshow that a lattice constant is in agreement with the lattice constantat the time of a perovskite structure in n≧22.

To a Si substrate, at the time of n≧4, above shows that the region whichfulfills “indispensable 3 conditions as an insulating film” does notexist, when it is made to grow epitaxially on Si substrate as expressedin FIG. 30. n =at the time of 2 and 3, the optimal small region A existsas expressed in FIG. 28 and FIG. 29.

On the other hand, on a strained Si substrate (in plus 1% of the case),since the conformity range shifts greatly, an optimum region (region B)appears also when it is n≧4 (FIG. 30). In this case, since it became RPtype, the energy of the part which goes up from the bottom of aconduction band is zero mostly, and the bottom of a conduction band willcorrespond to a barrier for electrons as it is. Since a barrier forelectrons will exceed 1.0 eV if the quantity of (Zr+Hf) is more thanhalf of the amount of B sites, a barrier for electrons is kept by it.Since it is in agreement when a lattice constant is a perovskitestructure, it becomes being the same as that of FIG. 23, and becomes anoptimum region in considerable, then n≧4 which time expressed to FIG. 30to the region B of FIG. 23.

Moreover, when n is larger than 4, it basically converges in the case ofa perovskite structure (FIG. 23). Because the ultimate AP structurewhere n becomes large infinitely, is a perovskite structure.

On the other hand, in n=2, a barrier for electrons (1 eV or more) isacquired in about 70% of lower range in the graph of FIG. 28. Therefore,in the strained Si of plus 1%, the portion of the region B of this FIG.will call it the optimum region which spread further from the optimumregion A in Si substrate.

Moreover, in n=3, about 60% of lower range turns into a range from whicha barrier for electrons (1 eV or more) is acquired in the graph of FIG.29. Therefore, in the strained Si of plus 1%, the region. of the regionB of this FIG. will call it the optimum region which spread further fromthe optimum region A in Si substrate.

FIG. 31 is a schematic diagram showing MOSFET which uses the RP typeinsulating film. That is, the source region S and the drain region D areformed on the surface of a silicon substrate or a strained Si substrate161. And the RP type insulating film 162 mentioned above is provided onthe channel region between the source region and the drain region, andthe gate electrode 163 is provided on it. MOSFET of low powerconsumption is realizable at high speed by using appropriately thematerial of the range of Region A or Region B expressed to FIG. 26through FIG. 30 as a material of the gate insulating film 162.

Next, referring to FIGS. 32 and 33, it is the gate insulating film whichgrew epitaxially on Si substrate or the strained Si substrate, and it is“the lamination structure (Ruddlesden-Popper type) of the rocksalt AOstructure and the perovskite ABO₃ structure”, and insulating film RP1and RP2 laminated by turns is explained.

Moreover, also in these graph, the contour lines S1-S6 of latticeconstants were expressed.

Here, since the energy levels of the next doors in a well differ, aninteraction is completely lost between the next wells, a band statedisappears, and a discrete-level appears. For this reason, the quantumwell insulating film using a discrete quantization level can be created,and the insulating film which has a very high barrier for electrons inall the regions expressed with the slash in FIG. 32 is obtained.

Moreover, since permittivity epsilon becomes higher than the case of RP1by mixing RP2, it is kept 20 or more in whole region. Therefore, it canoptimize only according to the conditions of a lattice constant, andRegion A turns into an optimum region to the Si. However, the regionwhich has overlapped with Region B is described as “A&B” here.

Ca₅(Ti_(0.5),Zr_(0.5))₃O₁₁ i.e., the substance which laminatedCa₂(Ti_(0.5),Zr_(0.5))O₄ and Ca₃(Ti_(0.5),Zr_(0.5))₂O₇ by turns is oneof the substances of an optimum.

Since the optimal lattice constant becomes large when the epitaxialgrowth on an about plus 1% strained Si substrate is considered, theoptimal region will shift from Region A. The lattice constant of thestrained Si with strain of plus 1% is 5.484 angstroms as expressed withthe contour line S3. In this case, it suits to the range of a contourline S4. The region which matches this lattice constant is the region Bof FIG. 32, and the region which has overlapped with Region A isdescribed as A&B. It turns out that the substance of a very large regionfunctions as a gate insulating film to strained Si.

If Ca₅(Ti_(0.4),Zr_(0.6))₃O₁₁ are used, the very ideal thin film whosebarrier for electrons is about 2.5 eV, whose lattice constant is 5.536angstroms and whose permittivity is about 40 can be created.

FIG. 33 is a summary of the lattice constant, the permittivity, thebarrier for electrons, etc. in the case of Hf is used for B site insteadof Zr. When Zr is compared with Hf, the lattice constant at the time ofusing Hf is smaller than that of Zr about 0.6%. That is, when Hf is usedcompared with the case of only Zr, an optimum region shifts somewhat,but there is no essential change.

FIG. 34 is a schematic diagram showing MOSFET using the insulating filmexpressed in FIGS. 32 and 33.

That is, the source region S and the drain region D are formed in thesurface of a silicon substrate or a strained Si substrate 171. And theRP type insulating film 172 mentioned above is provided on the channelregion between the source region and a drain regions and the gateelectrode 173 is provided on it. MOSFET of high speed and low powerconsumption is realizable by using appropriately the material of therange of Region A or Region B expressed in FIGS. 32 or 33 as a materialof the gate insulating film 172.

Next, referring to FIGS. 35 and 36, it is the gate insulating film grownepitaxially on Si substrate or the strained Si substrate, and theinsulating film of “the structure where the perovskite type substanceABO₃ and the two-layer nature AO layer of a rocksalt structure were madeto laminate” is explained. Moreover, also in these graph, the contourlines S1-S6 of a lattice constant were expressed.

In this lamination structure, a discrete level appears and the quantumwell insulating film using a quantization level can be created. As theresult, the insulating film which had a very high barrier for electronsis expected in all the regions expressed with the slash in FIG. 35.Since the energy state has leveled, it is as having already explainedthat the point that penetration probability becomes very small isimportant.

Furthermore, when two layers of AO layers are inserted, the B-O axis ofthe direction of thickness of ABO₃ will be in agreement. If this axis isin agreement, the dielectric characteristic will improve and the bigpermittivity epsilon will be obtained. For this reason, permittivityamounts to ten or more in all the regions of graph. In this structure,since the phase of ABO₃ is in agreement, this structure will be calledan In-Phase (IP) type. Moreover, according to the number n of layers ofthe perovskite type substance ABO₃ , it will express “IPn.”

That is, this example can be expressed as “IP1 structure.” According tothe matching condition of a lattice constant, the region A betweencontour lines S2 and S5 turns into an optimum region to Si. However, theregion which has overlapped with the region B which matches strained Siwas expressed as “A&B.”

In the case of Sr₃TiO₅ or Ca₃(Ti_(0.5),Zr_(0.5))O₅, the lattice constantof the insulating film coincides with the lattice spacing of Sisubstrate. Therefore, these materials are most suitable for epitaxialgrowth. Then, the permittivity epsilon is 34 and 20 respectively and islarge enough, and can be called one of the optimal substances as a gateinsulating film.

On the other hand, in the epitaxial growth on an about plus 1% strainedSi substrate, since the optimal lattice constant becomes large, theoptimal region shifts from Region A. The lattice constant of strained Siwith strain of plus 1% is 5.484 angstroms, and is expressed by thecontour line S3. The range which matches the lattice constant is betweencontour lines S4 and S6, and serves as Region B. Here, the region whichoverlapped with Region A was expressed as A&B. It turns out that thesubstance of a very large region functions as a gate insulating film tostrained Si. For example, in Ba₃TiO₅ or (Ba_(0.4),Sr_(0.6))₃ TiO₅ thebarriers for electrons are both about 2.5 eV, the lattice constants are5.56 and 5.48 angstroms respectively, and the permittivity epsilons areboth about 40, and a very ideal gate insulating film can be created.

FIG. 36 is a summary of the lattice constant, the permittivity and thebarrier for electrons, etc when Hf is used for B site instead of Zr.When Zr is compared with Hf, the lattice constant at the time of usingHf is smaller than that of Zr about 0.6%. That is, when Hf is usedcompared with the case of only Zr, an optimum region shifts somewhat,but there is no essential change. That is, when Hf is used compared withthe case of only Zr, an optimum region shifts somewhat, but there is noessential change.

It is necessary to note that the barrier for electrons is low whenvoltage is not applied to an insulating film in an IP1 type gateinsulating film. If voltage is added, the energy level in the well ofnext doors will shift, and a big barrier for electrons will be formed.On the other hand, the energy level of the well of next doors can alsobe designed to a different value When voltage is not applied. Forexample, what is necessary is just to combine IP1 type and IP2 type.This is the same with having mentioned above about double well structureor triple well structure, referring to FIG. 4 through FIG. 9.

Moreover, the present invention is not limited to IP1 type, but includesIP2 type, IP3 type, etc. In this case, if compared with IP1 type, apermittivity. epsilon will raise more and a lattice constant will becomelarger than IP1 type (It is mostly in agreement with the latticeconstant of a perovskite structure.) About a barrier for electrons, withIP2 type or IP3 type, since an energy level changes a lot in the well ofnext doors when thickness is thin, it is easy to use.

FIG. 37 is a schematic diagram showing MOSFET using the insulating filmexpressed in FIGS. 35 and 36. That is, the source region S and the drainregion D are formed in the surface of a silicon substrate or a strainedSi substrate 181. And the IPn type insulating film 182 mentioned aboveis provided on the channel region between the source region and a drainregion, and the gate electrode 183 is provided on it. MOSFET of highspeed and low power consumption is realizable by using appropriately thematerial of the range of Region A or Region B expressed in FIGS. 35 or36 as a material of the gate insulating film 182.

Next, it is the gate insulating film grown epitaxially on Si substrateor the strained. Si substrate, and the insulating film which made IP1type and IP2 type laminate by turns is explained referring to FIGS. 38and 39.

Also in this case, a discrete level appears and the quantum wellinsulating film using a quantization level can be created. In all theregions expressed with the slash in FIG. 38, an insulating film with avery high barrier for electrons is obtained. Since the energy state hasleveled, penetration probability becomes very small, as alreadyexplained. Moreover, permittivity epsilon amounts to 20 or more.

According to the adjustment conditions of a lattice constant, the regionA between contour lines S2 and S5 turns into an optimum region to Si.

Here, the region which has overlapped with Region B was expressed asA&B. In the case of (Ca_(0.25),Sr_(0.75))₇Ti₃O₁₃, the lattice constantof the insulating film coincides with the lattice spacing of Sisubstrate. Therefore, these materials are most suitable for epitaxialgrowth. Then, the permittivity epsilon is 50 and large enough, and canbe called one of the optimum substances.

On the other hand, in the epitaxial growth on an about. plus 1% strainedSi substrate, the optimal region shifts from Region A since the optimallattice constant becomes large. The lattice constant of strained Si withstrain of plus 1% is 5.484 angstroms, and is expressed with a contourline S3. The range which matches the lattice constant is the region Bbetween contour lines S4 and S6. Here, the region which overlapped withRegion A was expressed as A&B.

It turns out that the substance of a very large region functions as agate insulating film to strained Si. For example, if Sr₇Ti₃O₁₃ is used,a very ideal thin film whose barrier for electrons is about 2.5 eV,lattice constant is 5.47 angstroms, and permittivity epsilon is about 55can be created.

FIG. 39 is a summary of the lattice constant, the permittivity, thebarrier for electrons, etc. when Hf is used as B site instead of Zr.When Zr is compared with Hf. the lattice constant at the time of usingHf is smaller than that of Zr about 0.6%. That is, when Hf is usedcompared with the case of only Zr, an optimum region shifts somewhat,but there is no essential change.

It also turned out that a thin film whose leak current is very littleand permittivity epsilon is high can be created since the axis of a highdielectric layer (well layer) is assembled in the insulating film of anIPn type or type (IPn+IPm) (n, m integer). There may also be aninsulating film of an MIM capacitor as an example of application of thisinsulating film. Moreover, since there is a big effect also in Ferroelectricity when the axis is assembled even if it considers aferroelectric material thin film instead of a high dielectric, it ispossible to create a ferroelectric material thin film MIM capacitor withlittle leak current.

MIM capacitor structure was created by forming Ba₃TiOs thin film as afilm on SrRuO₃ electrode, and actually forming SrRuO₃ as a film as an upelectrode again. Since the in-plane strain was added in this case,ferroelectric material MIM capacitor whose leak current is very smallwith big polarization has been created.

Moreover, as a suitable capacitor for FeRAM (ferroelectric RAM), Pb(Zr,Ti)O₃ is famous. In the case, it is impossible to make PbO a barrier. Itis because a barrier for electrons cannot be raised even if some PbO isput in since the orbital energy is lower than Ti. However, it ispossible to put in (Ca, Sr, Ba)O instead of PbO. If it devises so that abarrier for electrons may go up and the axis of a dielectric layer maybe assembled by this insertion, it is possible to create an MIMcapacitor with big polarization and low leak current.

In the above, the optimum range of the insulating film using a layeredperovskite substance was explained. As a result of having given someexamples, the following things can say as a conclusion. As a result ofgiving some examples, it is important to make the level in a welldiscrete, devising of “making the well of next doors not to be the sameenergy level”, “thickening a barrier layer”, etc. And when theabove-mentioned device cannot be carried out, the range of the materialwhich can be used can be partly extended by using Zr and Hf as a B sitematerial. In a perovskite type and RP type, it is desirable to attainoptimization with devising B site.

Of course, the example shown here is a mere example and can considervarious film structures. All the film structures laminated whilechanging variously the thickness of a barrier layer and the thickness ofa well layer which are considered variously are included by the range ofthe invention.

Moreover, in the above explanation, following three were mentioned asconditions at the time of forming an insulating film. (1) Make mismatch(difference) of lattice constant into less than Plus-or-Minus 1.5% tosubstrate. (2) Barrier is high. (3) Permittivity is Large. Furthermore,you may also insert an insulating buffer layer between this insulatingfilm and substrate. In this case, especially an important point is apoint that a buffer layer does not necessarily need to fulfill theconditions of (2) which is most difficult to be filled. It is because arole assignment can be carried out as the insulating film laminated on abuffer layer bears the conditions of (2) and a buffer layer is made tobear the conditions of the improvement in the interface characteristic,i.e., (1), after fulfilling the conditions of (3) (high permittivity) asa whole as much as possible.

Such structure can be made just because the region of an insulating filmhas the composition and structure of this example. This buffer layer isvery effective when the interface characteristic wants to be improved.

If what has high permittivity is used as a buffer when voltage is added,since the potential drop in a buffer layer portion is suppressed moresmallish, it can create the first layer thickly rather than the timeonly of a barrier layer (namely, when there is no buffer layer). As aresult, the effect that the surface of the first layer can be madeflatter is acquired.

If a barrier layer is thickened, since permittivity will become small,and it becomes impossible to use as a gate insulating film in the casewhere there is no buffer layer and a barrier layer with low permittivityis directly grown up on a substrate to it. But if a barrier layer ismade thin too much, it will become very difficult to make a flat anduniform film, and leak current will get worse.

For example, the CeO₂ thin-film direct junction which grows epitaxiallygood on Si (111) side can be left on Si (111) substrate by starting withthe buffer layer CeO₂ (111), when creating quantum well structureSrO/CeO₂/SrO/CeO₂/SrO. Since the difference of the lattice constant ofSi substrate and CeO₂ is not filled to 1%, it is thought that a verygood interface is formed. Therefore, the structure which has CeO₂ inright above Si is effective.

It may begin to laminate from SrO, or may begin to laminate from CeO₂,or whichever is sufficient. It is an advantage that the material whichcan grow epitaxially with better interface quality can be chosen. Sincethe quantum well insulating film on it will bear the height of a barrierif it is a substance with high permittivity, it is that choosing only inthe interface characteristic is possible.

Here, there is a tendency for the barrier of materials with highpermittivity to be low. As a material of the above-mentioned bufferlayer, all the high dielectric thin film material, whose permittivity ishigh, and whose lattice constant is well in agreement in the latticeconstant of a silicon substrate (or strained Si substrate),but whosebarrier height for electrons is not high, will be considered as acandidate. As the example of representation, CeO₂, YSZ (Y₂O₃+ZrO₂), (Ba,Sr, Ca)O, SrTiO₃, Ca(Ti, Zr)O₃, (Ba, Sr, Ca)F₂, etc. can be mentioned.

EXAMPLE

Referring to drawings, some embodiments of the present invention willnow be described in more detail. The insulating film of the inventionproviding single quantum well structure or multi quantum well structurecan be manufactured by the sputtering method, the laser ablation method,the chemistry gaseous phase growing-up method (CVD), etc. In thefollowing examples, all of the thin film was grown up by the molecularbeam epitaxy (MBE) method.

First, the molecular beam epitaxy equipment used in. common will beexplained. The vacuum vessel is exhausted by the cryopump. The ultimatevacuum was 10⁻⁶ Pa or less. A substrate holder is provided in a vacuumvessel and a substrate is installed in this substrate holder.

The substrate holder is heated at a heater. Two or more Knudsen cellsare provided so that the substrate may be countered, and the cellshutter is provided in the opening of each Knudsen cell. In each Knudsencell, the metal of each element selected from the group consisting ofbarium (Ba), Strontium (Sr), calcium (Ca), cerium (Ce), a hafnium (Hf),a zirconium (Zr), titanium (Ti), tantalum (Ta), a ruthenium (Ru), alantern (La), a yttrium (Y), gadolinium (Gd), niobium (Nb), and vanadium(V) is filled. These metals are the composition metallic elements of thethin films to be formed in the following examples.

Moreover, in order that oxidation reaction required to obtain a thinfilm may occur, it is set up so that the pure ozone gas evaporated inthe liquid ozone storeroom may blow off from a nozzle and may irradiatea substrate. Between a nozzle and a substrate, an ozone shutter isinserted if needed.

First Example

First, MOSFET (MOS type field effect transistor) using the insulatingfilm which has the single quantum well structure of SrO/CeO₂/SrO as afirst example of the present invention will be explained.

FIG. 10 is a sectional view of the gate insulating-film of MOSFET of thefirst example of the present invention. That is, in FET of this example,the source region .S and the drain region D are formed in the surface ofa silicon substrate 11, and the gate electrode 16 is provided throughthe gate insulating film 12 on the channel region which is formedbetween them. A gate insulating film has the single quantum wellstructure where the SrO barrier layer 13, the CeO₂ well layer 14, andthe SrO barrier layer 15 are laminated.

Hereafter, the manufacture procedure of this insulating film 12 will beexplained in detail.

That is, first, the SrO (111) layer 13 was grown epitaxially on the Sisubstrate 11 whose major surface is (111). The thickness of the SrOlayer was made into about 7.5 angstroms. More specifically, first, onlystrontium (Sr) was grew for ⅓ ML (mono atomic layer: atomic layer) underthe environment where ozone was not applied, pressure was 10⁻⁷ Pa, andsubstrate temperature was 850 degrees centigrade. Then, SrO was formedas a film in the ozone flux 1.2×10¹² molecule/second cm² under theenvironment where pressure is 10⁻⁶ Pa and substrate temperature is 700degrees centigrade. ⅓ strontium (Sr) layer of ML manufactured in earlystages oxidized in this stage, and changed to the SrO layer.

Moreover, although it is confirmed by the experiment that it is alsopossible to form a film at about 200-degrees centigrade low temperature,since it is set as 700 degrees centigrade when forming CeO₂ as a film,forming a film at 700 degrees centigrade is chosen. If the substance ofthe portion of CeO₂ is able to form as a film at lower temperature or itbecomes possible to form CeO₂ as a film at lower temperature, a seriesof insulating-film structures can be created by forming a film at lowertemperature.

Next, only 4.7 angstroms of CeO₂ (111) layers 14 was formed as a film onthe SrO film formed as a film epitaxially. When forming this CeO₂ as afilm, the pressure was 10⁻⁶ Pa, substrate temperature was 700 degreescentigrade, and ozone flux was 8.8×10¹² molecule/second cm².

Furthermore, SrO (111) films 15 is grew epitaxially for only 7.5angstroms, under the environment where pressure is 10⁻⁶Pa, substratetemperature is 700 degrees centigrade and ozone flux is 1.2×10¹²molecule/second cm². And the gate electrode 16 was formed byvapor-depositing gold (Au) on it.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 6.5 angstroms. Moreover, the leak currentwhen applying the electric field of 5 MV/cm was a very small value of10⁻⁴ A/cm².

Incidentally, at the same EOT, the leak current of the gate thin filminsulator composed of CeO₂ or SiO₂ was 1 A/cm² , 10⁵ A/cm²(extrapolation value), respectively. That is, as for it, the insulatingfilm of these comparative examples turned out that leak current hasreached also 104 times and ¹⁰ ⁹ times as compared with this example.Thus, it turned out that the effect of having made quantum wellstructure in the insulating film is very large.

Furthermore, even if it used (Ba,Sr)O instead of the SrO films 13 and15, the same effect was attained. If this mixed crystal is used, alattice constant can be freely changed in the large range.

Therefore, when making it grow epitaxially, it becomes easier to matchthe lattice constant of the ground substrate.

In this example, when (Ba_(0.71),Sr_(0.29))O was grown epitaxially on Sisubstrate, the quality of the film of the barrier layers 13 and 15improved remarkably. The EOT became 4.3 angstroms when the same singlequantum well type gate insulating film as the above, i.e., the quantumwell insulating film of the structure of (Ba, Sr)O (9.4 A)/CeO₂ (4.7A)/(Ba, Sr)O (9.4 A), was created by making this thin film into abarrier layer.

This means that the high effect especially therefore produced has thevery large permittivity of (Ba, Sr)O compared with it of SrO. The leakcurrent when applying a big electric field of 5 MV/cm was a very smallvalue of 10⁻² A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁶ A/cm², and reached 10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure was very large.

When (Ba, Sr)O was used, compared with SrO, the interface level densityby strain of an interface was able to be reduced single or more figures.The use of this is large at the point which does not remain because itsays that it is easy to grow epitaxially on Si, but can control thedegree fall of mobility of the transistor by interface defects. By thistrial production, the mobility of a transistor showed 25% or more ofimprovement.

Second Example

Next, MOSFET using the insulating film which has the single quantum wellstructure of SrO/SrTiO₃ (it may omit following STO)/SrO as a secondexample of the. present invention will be explained.

FIG. 11 is a sectional view of the gate insulating film of MOSFET of thesecond example of the present invention.

That is, in FET of this example, the source region S and the drainregion D are formed in the surface of a silicon substrate 21, and thegate electrode 26 is provided through the gate insulating film 22 on thechannel region which is formed between them. A gate insulating film hasthe single quantum well structure where the SrO barrier layer 23, theSTO well layer 24, and the SrO barrier layer 25 were laminated.

This is explained in order of a manufacturing process. That is, first,the SrO (001) layer 23 was grown epitaxially on the Si substrate 21whose major surface is (001). The thickness of the SrO layer 23 was madeinto about 5.2 angstroms. More specifically, first, only strontium (Sr)was grew for ¼ ML (mono atomic layer: atomic layer) under theenvironment where ozone was not applied, pressure was 10⁷ Pa, andsubstrate temperature was 850 degrees centigrade. Then, SrO was formedas a film in the ozone flux 1.5×10¹² molecule /second cm² under theenvironment where pressure is 10⁻⁶ Pa and substrate temperature is 600degrees centigrade. ¼ strontium (Sr) layer of ML manufactured in earlystages oxidized in this stage, and changed to the SrO layer.

Next, only 3.9 angstroms. of SrTiO₃ (001) layers 24 was epitaxiallyformed as a film on it epitaxially. When forming this film, the pressurewas 10⁻⁶ Pa, substrate temperature was 600 degrees centigrade, and ozoneflux was 1.5×10¹² molecule/second cm².

Furthermore, SrO (001) films 25 is grew epitaxially for 5.2 angstroms.Since the conditions of film forming of SrO were able to be made thesame as that of SrTiO₃ film, it was made the completely same conditions.

And the gate electrode 26 was formed by vapor-depositing gold (Au) onit.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 4.1 angstroms. Moreover, the leak currentwhen applying the electric field of 5 MV/cm was a very small value of2×10⁻² A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁶ A/cm², and reached 5×10⁷ times of that of theabove-mentioned insulating film. From this, it has checked: that theeffect of having made quantum well structure in the insulating film wasvery large.

Third Example

Next, MOSFET in which the insulating film which has double quantum wellstructure called SrO/STO/SrO/STO/SrO is provided will be explained as athird example of the invention.

FIG. 12 is a sectional view of the gate insulating film of MOSFET of thethird example of the invention.

That is, in FET of this example, the source region S and the drainregion D are formed in the surface of a silicon substrate 31, and thegate electrode 38 is provided through the gate insulating film 32 on thechannel region which is formed between them. A gate insulating film hasthe double quantum well structure where the SrO barrier layer 33, theSTO well layer 34, the SrO barrier layer 35, the STO well layer 36, andthe SrO barrier layer 37 were laminated.

The manufacturing process of this is explained. That is, first, the SrO(001) layer 33 was grown epitaxially on the (001) Si substrate 31. Thethickness of the SrO layer 33 was made into about 7.8 angstroms. Morespecifically, first, only strontium (Sr) was grew for 1/4 ML (monoatomic layer: atomic layer) under the environment where ozone was notapplied, pressure was 10⁻⁷ Pa, and substrate temperature was 850 degreescentigrade. Then, SrO was formed as a film in the ozone flux 1.5×10¹²molecule/second cm² under the environment where pressure is 10⁻⁶ Pa andsubstrate temperature is 600 degrees centigrade.

Next, only 3.9 angstroms of SrTiO₃ (001) layers 34 was formed as a filmon it epitaxially. When forming this film, the pressure was 10⁻⁶ Pa,substrate temperature was 600 degrees centigrade, and ozone flux was1.5×10¹² molecule/ second cm².

Formation of the film of the SrO layer 35, SrTiO₃ 36 and the. SrO layer37 was performed under the same conditions as these conditions. That is,only 5.2 angstroms of SrO (001) film 35 was formed as a film on SrTiO₃layer 34 epitaxially.

Next, only 7.8 angstroms of the SrTiO₃ (001) layers 36 was formed as afilm on it epitaxially. Furthermore, SrO (001) films 37 is grewepitaxially for 7.8 angstroms. And the gate electrode 38 was formed byvapor-depositing.gold (Au) on it.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 8.3 angstroms.

Moreover, the leak current when applying the electric field of 5 MV/cmwas a very small value of 10⁻⁶ A/cm².

As a comparative examples the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10³ A/cm², and reached 10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

When voltage is applied, the state in two well layers 34 and 36 may bein agreement in energy as a special case. In such a case, it isnecessary to design gate structure, paying attention to this point sinceband offset falls. In this example, the phenomenon in which the leakcurrent increased rapidly in near the electric field of 5.7 Mv/cm wasseen. what is necessary is just to use it below by this electric fieldfundamentally. This situation can also be avoided by providing triplewell structure which will be explained in detail about the fifthexample.

Fourth Example

Next, the insulating film whose thickness of the double quantum wellstructure of the third example mentioned above will be explained as thefourth example of the invention.

That is, the lamination structure of the insulating film wasSrO/srTiO₃/srO/srTiO₃/srO.

The thickness of all of SrO layers was 5.2 angstroms, and the thicknessof all of SrTiO layers was 3.9 angstroms. The method of forming films isthe same as that of the third example.

In the case of the insulating.film of this example, the band offset wasabout 1 eV before the voltage is applied. However, since there wasalmost no interaction between well layers, the leak current whenapplying the big electric field of 5 MV/cm was the very small value of10⁻⁵ A/cm². That is, when voltage was applied, the band offset went upsubstantially.

Moreover, the equivalent. oxide thickness (EOT) of the obtainedinsulating film was a very small value of 6.2 angstroms.

The Fifth Example

Next, MOSFET in which the insulating film which has triple quantum wellstructure of SrO/STO/SrO/STO/SrO/STO/SrO is provided will be explainedas the fifth example of the invention.

FIG. 13 is a sectional view of the gate insulating film of MOSFET of thefifth example of the invention.

That is, in FET of this example, the source region S and the drainregion D are formed in the surface of a silicon substrate 41, and thegate electrode 410 is provided through the gate insulating film 42 onthe channel region which is formed between them. A gate insulating filmhas triple quantum well structure where the layers are laminated in thisorder of SrO barrier layer 43, the STO well layer 44, the SrO barrierlayer 45, the STO well layer 46, the SrO barrier layer 47, the STO welllayer 48, and the SrO barrier layer 49.

This manufacturing process will be explained. First, the SrO (001) layer43 was grown epitaxially on the Si substrate 41 whose major surface is(001).

The thickness of the SrO layer 43 was made into about 5.2 angstroms.More specifically, first, only strontium (Sr) was grew for ¼ ML (monoatomic layer: atomic layer) under the environment where ozone was notapplied, pressure was 10⁻⁷ Pa, and substrate temperature was 850 degreescentigrade. Then, SrO was formed as a film in the ozone flux 1.5×10¹²molecule /second cm² under the environment where pressure is 10⁻⁶Pa andsubstrate temperature is 600 degrees centigrade.

Next, only 3.9 angstroms of SrTiO₃ (001) layers 44 was formed as a filmon it epitaxially. When forming this film, the substrate temperature was600 degrees centigrade and the ozone flux was 1.5×10¹² molecule/secondcm².

Next forming films of SrO, SrTiO₃, SrO, SrTiO₃, and SrO was performedwhile these conditions were maintained.

That is, 5.2 angstroms of SrO (001) film 45 was formed as a film onSrTiO3 layer 44 epitaxially. Next, 7.8 angstroms of the SrTiO₃ (001)layers .46 was formed as a film on it epitaxially. Furthermore, 5.2angstroms of SrO (001) film 35 was formed as a film on SrTiO₃ layer 34epitaxially. Next, only 7.8 angstroms of the SrTiO₃ (001) layers 36 wasformed as a film on it epitaxially.

Furthermore, about 5.2 angstroms of the SrO (001) layer 49 was formed asa film on the SrTiO₃ layer 48 epitaxially. And the gate electrode 410was formed by vapor-depositing gold (Au) on it.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 8.4 angstroms. Moreover, the leak currentwhen applying the electric field of 5 MV/cm was a very small value of10⁻⁶ A/cm². This result is mostly in agreement with the result of theexample mentioned above.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10³ A/cm², and reached 10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

In triple well of the invention, also when the voltage was applied, thephenomenon in which the leak current increased rapidly was not seen.This point is the difference with the case of a double well.

The Sixth Example

Next, the MIM (metal, insulator, and metal) capacitor using theinsulating film of the invention will be explained as the sixth exampleof the invention.

FIG. 14 is a sectional view of the MIM capacitor. of this example. Thisstructure is explained in order of the manufacturing process.

First, although the major surface used MBE for (001) SrTiO₃ substrate 51and created the capacitor to it, structure was given to the gateinsulating film 52 at this time. Specifically, SrRuO₃ electrode 53 wasgrown epitaxially on SrTiO₃ substrate 51, and the SrO (001) layer 54 wasgrown epitaxially on it. The thickness of the SrO layer 54 was made intoabout 5.2 angstroms.

Next, the 3.9 angstroms of the SrTiO₃ (001) layers 55 was grewepitaxially on it. Furthermore, about 5.2 angstroms of SrO (001) layers56 of the as same thickness as that of the preceding was grownepitaxially on the SrTiO₃ layer 55 and SrRuO₃ electrode 57 was grownepitaxially on it.

Generally, the pressure was 10⁻⁶ Pa, the substrate temperature was 600degrees centigrade, and the ozone flux was 1.5×10¹² molecule/second cu².

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small value of 4.1 angstroms. Moreover, theleak current when applying the large electric field of 5 MV/cm was avery small value of 10⁻⁶ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 5×10⁷ A/cm², and reached 10⁶ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating filmcapacitor was very large.

The Seventh Example

Next, MOSFET in which the insulating film which has the single quantumwell structure of Ce-silicate/CeO₂/SrO will be explained as the seventhexample of the invention.

FIG. 15 is a sectional view of the gate insulating film of MOSFET of theseventh example of the invention.

That is, in FET of this example, the source region S and the drainregion D are formed in the surface of a 25 silicon substrate 61, and thegate electrode 66 is provided through the gate insulating film 62 on thechannel region which is formed between them. The gate insulating filmhas the single quantum well structure where layers were made laminatedin this order of the Ce-silicate (Si) barrier layer 63, the CeO2 welllayer 64, and the SrO barrier layer 65.

This manufacturing process.is explained.

First, the CeO₂ (111) layer 64 was grown epitaxially-on the Si substrate61 whose major surface is (111). Thickness of CeO2 layer was made intoabout 8.2 angstroms.

The surface of the Si substrate was Hydrogen-terminated by HF processingand NH₄F, and CeO₂ was formed as a film after an appropriate time. Whenforming CeO₂ as a film, the pressure was 10⁻⁶Pa, the substratetemperature was 700 degrees centigrade, and the ozone flux was 8.8×10¹²molecule /second cm². Next, 7.5 angstroms of the SrO (111) film 65 wasgrown epitaxially under the condition where the pressure is 10⁻⁶Pa, thesubstrate temperature is 700 degrees centigrade and the ozone flux is1.2×10¹² molecule/second cm². In this stage, oxygen annealing wasperformed for 30 seconds at 800 degrees centigrade.

At this time, Ce silicate barrier layer 63 grew up to be the thicknessof about 3.5 angstroms at the interface of Si and CeO₂. This barrierlayer was able to be used as the barrier of well structure. And the gateelectrode 66 was formed by vapor-depositing gold (Au) on it.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 3.8 angstroms. Moreover, the leak currentwhen applying the electric field of 5 MV/cm was a very small value of3×10⁻² A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁷ A/cm², and reached 3×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

Moreover, you may use the well layer in which La₂O₃, Y₂O₃, Gd₂O₃,SrTiO₃, etc. were grown epitaxially instead of CeO2. In these cases, itis possible respectively to make La silicate, Y silicate, Gd silicate,and SiO₂ by annealing as a thin film barrier layer, and quantum wellstructure can be formed.

The characteristic that it is possible to create EOT in thickness ofabout 4-6 angstroms in any case, and leak current becomes 10⁻²-about10⁻⁴ A/cm² is acquired. It means that the validity of quantum wellstructure was shown since. the improvement of 10⁸ to 10⁹ orders wasfound compared with the case of the SiO₂ same film of EOT.

The Eighth Example

Next, MOSFET in which the insulating film which has the single quantumwell structure of Hf-silicate/HfO₂/SrO is provided will be explained asthe eighth example of the invention.

FIG. 16 is a sectional view of the gate insulating film of MOSFET of theeighth example of the present invention.

That is, in FET of this example, the source region S and the drainregion D are formed in the surface of a silicon substrate 71, and thegate electrode 76 is provided through the gate insulating film 72 on thechannel region which is formed between them. The gate insulating filmhas the single quantum well structure in which the Hf-silicate. barrierlayer 73, the HfO2 well layer 74, and the SrO barrier layer 75 are madeto laminated in this order.

This manufacturing process will be expained.

First, the HfO₂ layer was grown on the Si substrate 71 whose majorsurface was (111).

At this time, the HfO2 layer did not carry out epitaxial growth but wasin the amorphous state. Although MBE equipment is used in this example,if it can be made to grow up in layers, CVD will also serve as theleading film forming technique, for example.

The thickness of HfO₂ layer was made into about 8.2 angstroms. Thesurface of the Si substrate 71 was Hydrogen-terminated by HF processingand NH₄F, and HfO₂ was formed as a film after an appropriate time.

At this time, the pressure was 10⁻⁶ Pa, the substrate temperature was700 degrees centigrade, and the ozone flux was 8.8×10¹² molecule/secondcm².

Next, the SrO (111) layer 75 was formed on this HfO₂ layer. In thiscase, 7.5 angstroms of the SrO (111) layer 75 was grown under thecondition where the pressure is 10⁻⁶Pa, the substrate temperature is 700degrees centigrade and the ozone flux is 1.2×10¹² molecule/second cm².In this stage, annealing in oxygen for 30 seconds was performed at 800degrees centigrade. By this annealing, Hf silicate layer 73 was able togrow up to be the thickness of 3.5 angstroms at the interface of the Sisubstrate 71 and HfO₂ layer 74, and this was able to be made into thebarrier layer of well structure. And the gate electrode 76 was formed byvapor-depositing gold (Au) on it.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 6.8 angstroms. Moreover, the leak currentwhen applying the electric field of 5 MV/cm was a very small value of10⁻⁴ A/cm².

As a comparative. example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁵ A/cm², and reached 10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

Moreover, even if it uses the amorphous thin film of ZrO₂, Al₂O₃, Ta₂O₃,TiO₂, the nitrides HfON, ZrON, and AlON and TaON, and TiON instead of aHfO₂ amorphous thin film to an interface with Si, it was possible tohave made Zr-silicate, Al-silicate, Ta-silicate, Ti-silicate,Hf-silicate, Zr-silicate, Al-silicate, Ta-silicate, and Ti-silicate,respectively, as thin film barrier structure, and it was possible tohave created well structure.

Furthermore, even if the amorphous thin film of SrTiO₃, the amorphousthin film of SrZrO₃, the amorphous thin film of mixed crystal Sr(Ti,Zr)O₃, the amorphous thin film of Sr₂Nb₂O₇, and the amorphous thin filmof Sr₂V₂O₇ instead of the HfO₂ amorphous thin film, it was possible tohave made SiO₂ thin film as thin film barrier structure to an interfacewith Si, and it was possible to have created well structure.

In any case, it is possible to create EOT to about 5-9 angstromsthickness, and the characteristic that leak current is 10⁻²-10⁻⁶ A/cm²is acquired. Since the 10⁸-10⁹ order grade improvement of the leakcurrent is carried out compared with the case of the SiO₂ film of EOT,it can be said that the validity of quantum well structure was shown.

The Ninth Example

Next, MOSFET in which the insulating film which has the single quantumwell structure of SrO/Ca(Ti, Zr)O₃ (it may omit following CTZO)/SrO isprovided will be explained as the ninth example of the invention.

FIG. 17 is a sectional view of the gate insulating film of MOSFET of theeighth example of the invention.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the strained Si-SOI (silicon oninsulator) substrate 81, and the gate electrode 86 is provided throughthe gate insulating film 82 on the channel region which is formedbetween them. The gate insulating film has the single quantum wellstructure where the SrO barrier layer 83, the CTZO well layer 84, andthe SrO barrier layer 85 was made to laminate in this order.

First, the formation method of strained Si-SOI will be explained below.

First, the SiGe buffer layer and the stress relaxation SiGe layer wereformed on Si substrate by CVD.

Next, pouring oxygen was performed by the SIMOX (separation by implantedoxygen) method. The dose amount of oxygen was. set to 4×10¹⁷ cm⁻². Then,by performing annealing at 1350 degrees centigrade for 6 hours, theembedded oxide film was formed into the first SiGe layer. At this time,in the bent SiGe layer, it embeds with SiGe in 1350-degree centigradehigh temperature annealing, and stress relaxation happens by the slideof the interface of an oxide film. Then, if a SiGe layer is oxidized bythe annealing in [of 1200 degrees centigrade] oxygen in order to makegermanium into high concentration, it will embed with SiGe andconcentration of germanium concentration will occur in the interfaceside with an oxide film. If etching removes the oxide film of thesurface, the SiGe thin film containing high-concentration germanium willbe formed. If Si is grown up by CVD on this film, Si thin film whichsensed the lattice constant of SiGe of a ground and was distorted willbe formed.. The strained Si-SIO substrate was created in this way.

Next, although a major surface uses MBE for the strained Si substrate 81of (001) and creates the gate insulating film 82 to it, structure isgiven to the gate insulating film 82 at this time. First, the SrO (001)layer 83 was grown epitaxially. The thickness of a SrO layer was madeinto about 5.2 angstroms. First, the hydrogen terminus of the Sisubstrate surface was carried out to HF processing by NH₄F, and,specifically, SrO was formed as a film on after an appropriate time.

Next, only Sr was grown for 2 ML under the environment where there wasno ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was lowtemperature of 200 degrees centigrade. Then, the ozone flux of 1.5×10¹²molecule/ second cm² was irradiated for 30 seconds under the environmentwhere the pressure was 10⁻⁶Pa and the substrate temperature was 200degrees centigrade. Thereby, two layers of SrO layers have been made(about 5.2 angstroms)

And, the Ca(Ti_(0.5),Zr_(0.5))O₃ (001) layers 84 was grown epitaxiallyon it for 3.9 angstroms. At this time, the pressure was 10⁻⁶Pa, thesubstrate temperature was 600 degrees centigrade, and the ozone flux was1.5×10¹² molecule /second cm². Furthermore, the SrO (001) film 85 wasgrown epitaxially on the Ca(Ti_(0.5),Zr_(0.5))O₃ film for 5.2 angstroms.Since the growth conditions of the SrO film were able to be made thesame as that of the Ca(Ti_(0.5),Zr_(0.5))O₃ film, it was completely madethe same. Gold was formed as a film on it by vapor deposition as thegate electrode 86.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm was a very small value of 3.2 angstroms. Moreover, the leak currentwhen applying a big electric field of 5 MV/cm was as small as5×10^(−2 A/cm) ².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁷ A/cm², and reached 2×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

This example showed that the gate insulating film with quantum wellstructure could also be adapted for MOSFET using a strained Si-SOIsubstrate.

Moreover, it was also possible to use (Ba, Sr, Ca)O instead of the SrOfilm. Since it was made possible to change the lattice constant withinquite large limits, it became easy to unite the lattice constant of aground surface when growing it epitaxially.

When it was made to grow epitaxially on the strained Si substrate using(Ba_(0.85),Sr_(0.15))O mentioned above, the membranous of the barrierimproved remarkably. EOT became 2.8 angstroms when the same well typegate insulating film as the above was constituted by making this thinfilm into a barrier layer. The leak current when applying the bigelectric field of 5 MV/cm was as small as 6×10⁻² A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 2×10⁷ A/cm², and reached 3×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large.

By using (Ba, Sr) O for an insulating film, the interface level densityby strain of an interface can be reduced 1/10 or less of that of SrO.Consequently, the mobility of a transistor could be prevented fromfalling by the interface level and the mobility has been improved 20%.or more.

The Tenth Example

Next, MIM in which the insulating film which has the single quantum wellstructure of SRO/BSO/BSTO/BSO/SRO is provided will be explained as thetenth example of the present invention.

FIG. 18 is a sectional view of the MIM capacitor of this example.

Hereafter, this MIM capacitor will be explained according to themanufacturing process.

First, the SrTiO₃ layer 98 was grown epitaxially on the Si substrate 91whose major surface was (001).

The surface of the Si substrate was Hydrogen-terminated by HF processingand NH₄F, and SrO was formed as a film after an appropriate time. Next,only Sr was grown for 1 ML under the environment where there was noozone, the pressure was 10⁻⁷ Pa and the substrate temperature was lowtemperature of 200 degrees centigrade. Then, the ozone flux of 1.5×10¹²molecule/second cm² was irradiated for 15 seconds under the environmentwhere the pressure was 10⁻⁶ Pa and the substrate temperature was 200degrees centigrade. Thereby, one layer of the SrO was made. Aftergrowing Ti for 1 ML on it, the same ozone flux as the above wasirradiated for 20 seconds. Then, TiO₂ film was grown for 1 ML. Byrepeating this process, the SrTiO₃ thin film was grown epitaxially onSi.

Next, the SrRuO₃ electrode 93 was grown epitaxially on the SrTiO₃ andthe (Ba_(0.75),Sr_(0.25))O (001) layer 94 was grown epitaxially on theSrRuO₃ electrode 93. The thickness of (Ba, Sr) O layers was made intoabout 5.4 angstroms. The (Ba 0.2, Sr0.8) TiO₃ (001) layer 95 was grownepitaxially for 3.95 angstroms on it. Only about 5.4 angstroms only ofas same the thickness as the point grew the (Ba_(0.75),Sr_(0.25))O (001)layer 96 was grown epitaxially on the (Ba, Sr)TiO₃ film for the same 5.4angstroms as the above. And the SrRuO₃ electrode 97 was grownepitaxially on the (Ba_(0.75),Sr_(0.25))O (001) layer 96. The formingcondition of the portion of capacitor was made that the pressure was10⁻⁶ Pa, the substrate temperature was 600 degrees centigrade, and theozone flux is 1.5×10¹² molecule/second cm².

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small value of 2.1 angstroms. Moreover, theleak current when applying a big electric field of 5 MV/cm was as smallas 10⁻¹ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁸ A/cm², and reached 10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

In particular, the permittivity of the barrier layer (Ba_(0.75),Sr_(0.25)) O is 20 or more, the permittivity of the thin well layer(Ba_(0.2), Sr_(0.8)) TiO₃ currently quantized is 500 or more, andpermittivity is very large. Therefore, it turns out that it is veryeffective that the leak current comes to be stopped by quantization.

As a comparative example, the capacitor in which the thickness of(Ba_(0.2), Sr_(0.8)) TiO₃ is 32 angstroms was made. Then, the equivalentoxide thickness (EOT) of the obtained insulating film capacitor was avery small value of 2.4 angstroms.

Moreover, the dielectric breakdown was carried out when the leak currentwhen applying the big electric field of 5 MV/cm was measured. From this,it is surmised that the leak current has reached the very big value of10⁹ A/cm² or more.

Moreover, in this comparative example, the leak current in the same EOTas this example when 5 MV/cm is applied by extrapolation is 10⁸ A/cm²,and it turned out that the performance has rather fallen. This isconsidered to be because for the energy level not to be quantized in thequantum well though it is the same lamination structure.

That is, the zero-point-vibration energy inside a well is 0.036 eV, andit is considered that the effective rise of band offset is hardlyacquired in the structure of this comparative example. Moreover, theinterval of the level of quantization is also 0.1 eV order, and anenergy level overlaps mutually and continues a level at the temperaturebeyond room temperature. That is, it turned out that it cannot but stopthe leak current by thickening the thickness although the permittivityfalls in the capacitor of the lamination structure where thequantization effect is not seen.

The Eleventh Example

Next, MIM in which the insulating film which has double quantum wellstructure called SRO/BSO/BSTO/BSO/BSTO /BSO/SRO is provided will beexplained as the eleventh example of the present invention.

FIG. 19 is a sectional view of the MIM capacitor of this example.

Hereafter, this MIM capacitor will be explained according to themanufacturing process.

The capacitor was made using MBE on the (001) Si substrate 101. That is,the SrTiO₃ layer 1010 was grown epitaxially on Si by the same method asthe tenth example. And the SrRuO₃ electrode 103 was grown epitaxially onthe SrTiO₃ layer 1010 and the (Ba_(0.75),Sr_(0.25))O (001) layer 104 wasgrown epitaxially on the SrRuO₃ electrode 103. The thickness of the (Ba,Sr)O layers was made into about 5.4 angstroms.

And, the (Ba_(0.2),Sr_(0.8))TiO₃ (001) layers 105 was grown epitaxiallyfor 3.95 angstroms on the (Ba, Sr) O layers. Furthermore, the(Ba_(0.75),Sr_(0.25))O (001) film 106 was grown epitaxially on this (Ba,Sr) TiO₃ film for the same 5.4 angstroms as the above. Furthermore, the(Ba_(0.2),Sr_(0.8))TiO₃ (001) layers 107 was grown epitaxially for 7.9angstroms on the (Ba_(0.75),Sr_(0.25))O (001) film 106. Furthermore, the(Ba_(0.75),Sr_(0.25))O (001) film. 108 was grown epitaxially on this(Ba, Sr)TiO₃ film for the same 5.4 angstroms as the above and the SrRuO3electrode 109 was grown epitaxially on the (Ba_(0.75),Sr_(0.25))O (001)film 108.

The forming condition of the portion of capacitor was made that thepressure was 10⁻⁶ Pa, the substrate temperature was 600 degreescentigrade, and the ozone flux is 1.5×10¹² molecule/second cm².

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small value of 3.3 angstroms. Moreover, theleak current when applying a big electric field of 5 MV/cm was as smallas 5×10⁻³ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁷ A/cm², and reached 2×10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Furthermore, as a modification of this example, the insulating film ofthe triple quantum well structure was made by growing(Ba_(0.75),Sr_(0.25))O (001) for 5.4 angstroms, growing (BaO.2, SrO.8)TiO₃ (001) for 3.95 angstroms and growing the SrRuO₃ electrode on it inthe double quantum well structure of this example.

The equivalent oxide thickness (EOT) of the obtained insulating filmcapacitor was a very small value of 4.3 angstroms. Moreover, the leakcurrent when applying a big electric field of 5 MV/cm was as small as5×10⁻⁴ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁶ A/cm², and reached 2×10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

The Twelfth Example

Next, MIM in which the insulating film which has the single quantum wellstructure of SRO/Al₂O₃/HfO₂/Al₂O₃/ SRO is provided will be explained asthe twelfth example of the invention.

FIG. 20 is a sectional view of the MIM capacitor of this example.

Hereafter, this structure will be explained according to themanufacturing process.

The capacitor was made using MBE on the (001) Si substrate 111. That is,the SrTiO₃ layer 118 was grown epitaxially on Si by the same method asthe tenth example. And the SrRuO₃ electrode 113 was grown epitaxially onthe SrTiO₃ layer 118 and the Al₂O₃ layer 114 was grown on the SrRuO₃electrode 113. Then, Al₂O₃ was an amorphous thin film,. and made thethickness of Al₂O₃ layers into 5 angstroms. And, the HfO₂ layer 115 wasformed as a film in layers for 5 angstroms on the Al₂O₃ layer 114. And,the Al₂O₃ layer 116 was formed as a film in layers for the same 5angstroms as the above on the HfO₂ layer 115.

The condition of forming the portion of capacitor was made that thepressure was 10⁻⁶ Pa, the substrate temperature was 400 degreescentigrade, and the ozone flux was 1.5×10¹² molecule/second cm². Thatis, since it is film forming at low temperature, it is very effective asa process of manufacturing capacitors.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small value of 4.8 angstroms. Moreover, theleak current when applying a big electric field of 5 MV/cm was as smallas 10⁻³ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 5×10⁵ A/cm², and reached 5×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Moreover, by using the amorphous thin films of ZrO₂, Ta₂O₃, TiO₂ andtheir nitrides HfON, ZrON, TaON, TiON, SrTiO₃, SrZrO₃ and their mixedcrystal Sr(Ti, Zr)O₃, Sr₂Nb₂O₇, Sr₂V₂O₇ instead of the amorphous thinfilm of HfO₂, the completely same well structure was able to be made.

On the other hand, in the thin film of the above-mentioned well portion,other materials as a barrier portion were also able to be used. Althougha prototype was built in this example by combining each of an (Ba, Sr,Ca)O, SiON, Hf-silicate, Zr-silicate, and Ti-silicate amorphous thinfilm to the above-mentioned substance as an extremely stable substance,in any case, EOT can be created to about 4-9 angstroms, and thecharacteristic that leak current is 10⁻²-about 10⁻⁶ A/cm² is acquired.It means that the validity of quantum well structure was shown since theimprovement of 10⁸ to 10⁹ orders was found compared with the case of theSiO₂ same film of EOT.

The Thirteenth Example

Next, MIM in which the insulating film which has double quantum wellstructure of SRO/Al₂O₃/ HfO₂/Al₂O₃/ HfO₂/ Al₂O₃/SRO is provided will beexplained as the thirteenth example of the present invention.

FIG. 21 is a sectional view of the MIM capacitor of this example.Hereafter, this capacitor will be explained, referring to themanufacturing process.

The capacitor was made using MBE on the Si substrate 121 whose majorsurface is (001). That is, the SrTiO₃ layer 1210 was grown epitaxiallyon Si by the same method as the tenth example. And the SrRuO₃ electrode123 was grown epitaxially on the SrTiO₃ layer 1210 and the Al₂O₃ layer124 was grown on the SrRuO₃ electrode 123. Then, Al₂O₃ was an amorphousthin film, and made the thickness of Al₂O₃ layers into 5 angstroms.

And, the HfO₂ layer 125 was formed as a film in layers for 5 angstromson the Al₂O₃ layer 124. And, the A₂O₃ layer 126 was formed as a film inlayers for the same 5 angstroms as the above on the HfO₂ layer 125.

And, the HfO₂ layer 127 was formed as a film in layers for 10 angstromson the Al₂O₃ layer 126 and the Al₂O₃ layer 128 was formed as a film inlayers for 5 angstroms on the HfO₂ layer 127.

Thus, the double quantum well structure was made into the insulator 122of the MIM capacitor. Finally, the SrRuO₃ electrode 129 was formed for50 angstroms. The condition of forming the portion of capacitor was madethat the pressure was 10⁻⁶Pa, the substrate temperature was 400 degreescentigrade, and the ozone flux is 1.5×10¹² molecule/second cm². That is,since it is film forming at low temperature, it is very effective as aprocess of manufacturing capacitors.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small.value of 8.1 angstroms. Moreover, theleak current when applying a big electric field of 5 MV/cm was as smallas 10⁻⁶ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10³ A/cm², and reached 10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Moreover, by using the amorphous thin films of ZrO₂, Ta₂O₃, TiO₂ andtheir nitrides HfON, ZrON, TaON, TiON, SrTiO₃, SrZrO₃ and their mixedcrystal Sr(Ti, Zr) O₃, Sr₂Nb₂O₇, Sr₂V₂O₇ instead of the amorphous thinfilm of HfO₂, the completely same well structure was able to be made. Onthe other hand, in the thin film of the above-mentioned well portion,other materials as a barrier portion were also able to be used. Althougha prototype was built in this example by combining each of an (Ba, Sr,Ca)O, SiON, Hf-silicate, Zr-silicate, and Ti-silicate amorphous thinfilm to the above-mentioned substance as an extremely stable substance,in any case, EOT can be created to about 4-10 angstroms and thecharacteristic that leak current is 10³-about 10⁻⁸ A/cm² is acquired. Itmeans that the validity of quantum well structure was shown since theimprovement of 10⁹ orders was found compared with the case of the SiO₂same film of EOT.

The Fourteenth Example

Next, MIM in which the insulating film which has the triple quantum wellstructure of SRO/Al₂O₃/HfO₂/Al₂O₃/ HfO₂/Al₂O₃/ HfO₂/ Al₂O₃/ SRO isprovided will be explained as the fourteenth example of the presentinvention.

FIG. 22 is a sectional view of the MIM capacitor of this example.Hereafter, this capacitor will be explained, referring to themanufacturing process.

The capacitor was made using MBE on the Si substrate 131 whose majorsurface is (001). That is, the SrTiO₃ layer 1312 was grown epitaxiallyon Si by the same method as the tenth example. And the SrRuO₃ electrode133 was grown epitaxially on the SrTiO₃ layer 1312 and the Al₂O₃ layer134 was grown on the SrRuO₃ electrode 133. Then, Al₂O₃ was an amorphousthin film, and made the thickness of Al₂O₃ layers into 5 angstroms.

And, the HfO₂ layer 135 was formed as a film in layers for 4 angstromson the Al₂O₃ layer 134. And, the Al₂O₃ layer 136 was formed as a film inlayers for the same 3.7 angstroms as the above on the HfO₂ layer 135.

And, the HfO₂ layer 137 was formed as a film in layers for 8 angstromson the Al₂O₃ layer 136 and the Al₂O₃ layer 138 was formed as a film inlayers for 3.7 angstroms on the HfO₂ layer 137. And, the HfO₂ layer 139was formed as a film in layers for 4 angstroms on the Al₂O₃ layer 138and the Al₂O₃ layer 1310 was formed as a film in layers for 3.7angstroms on the HfO₂ layer 139.

Thus, the triple quantum well structure was made into the insulator 132of the MIM capacitor. Finally, the SrRuO₃ electrode 1311 was formed for50 angstroms.

The condition of forming the portion of capacitor was made that thepressure was 10⁻⁶Pa, the substrate temperature was 400 degreescentigrade, and the ozone flux is 1.5×10¹² molecule/second cm². That is,since it is film forming at low temperature, it is very effective as aprocess of manufacturing capacitors.

Thus, the equivalent oxide thickness (EOT) of the obtained insulatingfilm capacitor was a very small value of 9.7 angstroms. Moreover, theleak current when applying the big electric field of 5 MV/cm was assmall as 5×10⁻⁸ A/cm² or less.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10² A/cm², and reached 2×10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Moreover, by using the amorphous thin films of ZrO₂, Ta₂O₃, TiO₂ andtheir nitrides HfON, ZrON, TaON, TiON, SrTiO₃, SrZrO₃ and their mixedcrystal Sr(Ti, Zr)O₃, Sr₂Nb₂O₇, Sr₂V₂O₇ instead of the amorphous thinfilm of HfO₂, the completely same well structure was able to be made.

On the other hand, in the thin film of the above-mentioned well portion,other materials as a barrier portion were also able to be used. Althougha prototype was built in this example by combining each of an (Ba, Sr,Ca)O, SiON, Hf-Silicate, Zr- Silicate, and Ti- Silicate amorphous thinfilm to the above-mentioned substance as an extremely stable substance,in any case, EOT can be created to about 8-10 angstroms, and the 10⁻⁶-orless 10⁻⁸ A/cm² characteristic is acquired for leak current. It meansthat the validity of quantum well structure was shown since theimprovement of 10⁹ or more orders was found compared with the case ofthe SiO₂ same film of EOT.

As mentioned above, there are various combinations of substances used asa well layer or a barrier layer in the first through 14th examples ofthe invention. Because wells (or barriers) are not always composed ofsame substance in the trial production of insulators. If quantum wellstructure can be made, it was proved as compared with the SiO₂insulating film that leak current can be controlled extraordinarily.

According to the embodiment of the invention, it turned out that thereis very big flexibility in the combination of material. Therefore, it ispossible to look for the combination equipped with the requiredcharacteristic very broadly.

The Fifteenth Example

Next, the MOSFET in which the material which is corresponds to theregion B expressed in FIG. 23 and FIG. 24 is provided as an insulatingfilm will be explained as the fifteenth example of the invention.

As an example of creation of actual MOSFET structure, although the caseof Ca(Ti_(0.4),Zr_(0.6))O₃ is described, if it is in this region B, itwas possible to make the MOSFET which has the characteristic that thepermittivity is large, the leak current is small and the mobility islarge.

FIG. 25 is a sectional view of the gate insulating-film of MOSFET of theexample of the invention.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the (001) strained Si substrate151. And the gate electrode 153 is provided through the gate insulatingfilm 152 on the channel region formed between these regions. The gateinsulating film is a thin film of the perovskite structure which isformed in the form where a CaO layer touches the silicon substrate andis expressed with Ca(Ti_(0.4),Zr_(0.6))O₃. The manufacturing method ofthe strained Si substrate is a method described in the ninth example.And the amount of the strain at this time was +1%. Also in subsequentexamples, the strained Si substrate which has the strain of +1% will beused. Hereafter, a film forming process is explained briefly.

First, the CaO layer was grown epitaxially on the (001) Si substrate andthe strained Si substrate using MBE. The surface of the Si substrate wasHydrogen-terminated by HF processing and NH₄F, and CaO was formed as afilm after an appropriate time. Although the planarizing of thesubstrate included many processing, the planarizing of the substrateused here was processing to a grade in which atomic steps did not appearin all over the gate insulating film. Since the region of the gateinsulating film is becoming. small now, the present processing methodmay be enough for planarizing processing.

The CaO thin film was grown for 1 ML under the environment where thereis no ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was200 degrees ° C., and the ozone flux 1.5×10¹² molecule/second cm² wasirradiated to the film for 15 seconds under the environment where thepressure was 10⁻⁶ Pa and the substrate temperature was 200 degreescentigrade. Thereby, one layer of CaO layers was made. After growing themetal (Ti, Zr) for 1 ML on it so that Ti:Zr=0.4:0.6, the same ozone fluxas the above was irradiated for 20 seconds. Then, (Ti_(0.4),Zr_(0.6))O₂film was grown for 1 ML. By repeating this process,Ca(Ti_(0.4),Zr_(0.6))O₃ thin film was grown epitaxially on the strainedSi substrate.

Thus, finally the Ca(Ti_(0.4),Zr_(0.6))O₃ thin film was grownepitaxially for 51 angstroms by real thickness. It was a thin gateinsulating film with the thickness converted into SiO₂ thickness (EOT)of 5.0 angstroms, where the permittivity was about 40. Moreover, theleak current when applying a big electric field of 5 MV/cm was as smallas 8×10⁻² A/cm². This is because the real thickness is as thick as 51angstroms.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 5×10⁵ A/cm², and reached 6×10⁶ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofCa(Ti_(0.4),Zr_(0.6))O₃ was very large. Moreover, in the case of the(Sr_(0.5),Ca_(0.5))TiO₃ thin film, the leak current of the same order asthe case of SrTiO₃ will flow. That is, it was proved that although thelattice constant was well in agreement with the lattice constant of +1%of strained Si substrate, the barrier for electrons was almost equal tozero in (Sr_(0.5),Ca_(0.5))TiO₃ thin film.

Next, the effect of the lattice constant of the gate insulating filmbeing in agreement with the lattice constant of the substrate wasinvestigated. The interface electric charge trap densities Dit (cm⁻²/eV)of MOSFET made on the strained Si substrate were a quite low value of4×10¹¹cm⁻²/eV. Although this value is larger than the latest best valueof 10¹⁰ cm⁻²/eV at SiO₂/Si interface, it is a quite desirable value. Theeffect of the lattice constant of the gate insulating film being inagreement with the lattice constant of the substrate and using thestrained Si substrate enables the mobility being 750 (cm²/Vsec) at themaximum. This value is a desirable value when the lattice constant islarger for about plus 1%. If the lattice constant of the gate insulatingfilm can be made more in agreement with the lattice constant of thesubstrate, a better mobility value is expectable. However, since thebarrier for electrons is not kept large enough in the perovskitestructure as expressed in FIG. 23 and FIG. 24, the lattice constantcannot be made in agreement in the gate insulating film for MOSFET.

On the other hand, henceforth [the example 16 explained below], since alattice constant can be made well in agreement now, change of mobilitycan be explained. If the lattice constant of the gate insulating filmexceeds plus 1.5% to the substrate lattice constant, the interfaceelectric charge trap will increase rapidly. If the lattice constant ofthe gate insulating film exceeds plus 2% to the substrate latticeconstant, the interface electric charge trap will amount to 10¹⁴cm⁻²/eV. Therefore, it is necessary to. make the lattice constant of thegate insulating film less than +1.5%.

The Sixteenth Example

Next, the MOSFET in which the material which is correspond to the regionA or the region B expressed in FIG. 26 is provided as the insulatingfilm will be explained as the sixteenth example of the invention.

FIG. 27 expresses the result of having introduced Hf. As a result of thefollowing examples' creating and comparing MOSFET in parallel, there wasalmost no difference with the case of Zr.

In FIG. 26, the region A expresses the range of the optimum material tothe epitaxial growth on a silicon substrate, and the region B expressesthe range of the optimum material to the epitaxial growth on a plus 1%strained Si substrate. The case of Ca₂(Ti_(0.5),Zr_(0.5))O₄ as anexample of creation of actual MOSFET structure in this example 16. Thecase on a silicon substrate and the case on a plus 1% strained. Sisubstrate will be explained as this example. It was possible to make theMOSFET which has the characteristic that the permittivity is large, theleak current is small and the mobility is large.

FIG. 31 is a sectional view of the gate insulating-film of MOSFET of theexample of the present invention. Since the structure is the same evenif the strain of the substrate changes, the case of the siliconsubstrate or the plus 1% strained Si substrate is expressed.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the (001) Si substrate or thestrained Si substrate 161. And the gate electrode 163 is providedthrough the gate insulating film 162 on the channel region formedbetween these regions. The gate insulating film is a thin film of theperovskite structure which is formed in the form where a CaO layertouches the silicon substrate and is expressed withCa₂(Ti_(0.5),Zr_(0.5))O₄. The thickness of a perovskite portion is onelayer, and the index of RP type structure is 1 and is a RP1 type thinfilm.

The manufacturing method of the strained Si substrate was a methodmentioned above about the example 9.

And at this time the amount of strain was plus 1%. Also in subsequentexamples, the strained Si substrate which has the plus 1% amount ofstrain is used. Hereafter, the film forming process is explainedbriefly.

First, the CaO layer was grown epitaxially on the (001) Si substrate andthe strained Si substrate using MBE. The surface of the Si substrate andthe surface of the strained Si substrate were Hydrogen-terminated by HFprocessing and NH₄F, and CaO was formed as a film after an appropriatetime. Although the planarizing of the substrate included manyprocessing, the planarizing of the substrate used here was processing toa grade in which atomic steps did not appear in all over the gateinsulating film. Since the region of the gate insulating film isbecoming small now, the present processing method may be enough forplanarizing processing.

The CaO thin film was grown for 2 ML under the environment where thereis no ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was200 degrees centigrade, and the ozone flux 1.5×10¹² molecule/second cm²was irradiated to the film for 30 seconds under the environment wherethe pressure was 10⁻⁶ Pa and the substrate temperature was 200 degreescentigrade. Thereby, two layers of CaO layers were made. After growingthe metal (Ti, Zr) for 1 ML on it so that Ti:Zr=0.5:0.5, the same ozoneflux as the above was irradiated for 20 seconds. Then,(Ti_(0.5),Zr_(0.5))O₂ film was grown for 1 ML. By repeating thisprocess, Ca₂(Ti_(0.5),Zr_(0.5))O₄ thin film was grown epitaxially on thesilicon substrate and the strained Si substrate.

Thus, finally the Ca₂ (Ti_(0.5),Zr_(0.5))O₄ thin film was grownepitaxially for 51 angstroms by real thickness.

It was a thin gate insulating film with the thickness converted intoSiO₂ thickness (EOT) of 6.6 angstroms, where the permittivity was about31. Moreover, the leak current when applying a big electric field of 5MV/cm was as small as 4×10² A/cm². This is because the real thickness isas thick as 51 angstroms. On the no-strained silicon substrate, the leakcurrent increased not a little to the twice value of 8×10⁻² A/cm². Thisis because of the noise accompanying the increase in an interfaceelectric charge trap.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁵ A/cm², and reached 2.5×10⁶ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofCa₂(Ti_(0.5),Zr_(0.5))O₄ was very large.

Moreover, in the case of Sr₂TiO₄ thin film, in the same EOT, it remainsin the improvement of about single figure compared with the case ofSiON. That is, although the lattice constant is well in agreement withthe lattice constant of +1% of strained Si substrate in Sr₂TiO₄ thinfilm, it means that it was proved that the barrier for electrons is notfully improved.

Next, the effect of the lattice constant of the gate insulating filmbeing in agreement with the lattice constant of the substrate wasinvestigated. The interface electric charge trap densities Dit (cm⁻²/eV)of MOSFET made on the strained Si substrate were a quite low value of 10¹¹ cm⁻²/eV. Although this value is larger than the latest best value of10¹⁰ cm⁻²/eV at SiO₂/Si interface, it is a quite desirable value. Theeffect of the lattice constant of the gate insulating film being inagreement with the lattice constant of the substrate and using thestrained Si substrate enables the mobility being 850 (cm²/Vsec) at themaximum. This value is the desirable value acquired since the latticeconstant was in agreement with the lattice constant of the strained Sisubstrate. On the other hand, the interface electric charge trap densityDit (cm/⁻²/eV) of MOSFET on the no-strained silicon substrate was 4×10¹¹cm²/eV. Since there was about 1% of deviation of the lattice constant,the interface electric charge trap density Dit was somewhat large.However, it was a still very desirable value. Although the mobilitydidn# t rise by strain since Si substrate was used, the mobility of 435(cm²/Vsec) was realized at the maximum. This value can be called adesirable value if it takes into consideration that the lattice constanthas shifted from the lattice constant of the silicon. substrate about1%.

If the lattice constant of the gate insulating film can be made more inagreement with the lattice constant of the substrate even if on thesilicon substrate, the more desirable value of mobility is expectable.What is necessary to keep the barrier for electrons large enough is justto form for example, Ca₂(Ti_(0.25), Zr_(0.75))O₄ thin film in RP1 typestructure, as shown in FIG. 26 and FIG. 27. In this case, as formobility, 505 (cm²/Vsec) is realized at the maximum.

If the lattice constant of the gate insulating film exceeds plus 1.5% ofthe substrate lattice constant, the interface electric charge trap willincrease rapidly to 10¹⁵ cm⁻²/eV when the lattice constant is +2%.Therefore, it is necessary to keep the lattice constant of the gateinsulating film less than plus 1.5%.

Also in RPn (n =2, 3, 4, . . . ) type gate insulating film, if thematerial in the optimum region shown in FIGS. 28 and 29 is used, theimprovement of the same order in the characteristic of the leak currentas the above will be seen. For example, as for the maximum of themobility, 850 to 700 cm²/Vsec is obtained on the strained Si substrate,and 505 to 400 is obtained on the Si substrate. When the difference ofthe lattice constant of the gate insulating film and the latticeconstant of the substrate exceeds 1.5%, the interface electric chargetrap increases rapidly to 10¹⁴ cm⁻²/eV at plus 2%, and the mobilitydecreases rapidly to below 225 cm²/Vsec even on the strained Sisubstrate.

The Seventeenth Example

Next, the MOSFET in which the material which is corresponds to theregion A or Region B expressed in FIG. 32 is provided as the insulatingfilm will be explained as the seventeenth example of the presentinvention. FIG. 33 expresses the case where Hf is introduced. As aresult of creating MOSFET in parallel and comparing in the followingexample, there was almost no difference between the case of Zr and thecase of Hf.

In FIG. 32, the region A expresses the range of materials optimum in theepitaxial growth on the silicon substrate and the region B expresses therange of materials Optimum in the epitaxial growth on the +1% strainedSi substrate.

As an example of actual MOSFET structure, the structure whereCa₅(Ti_(0.5), Zr_(0.5))₃O₁₁, i.e., Ca₂(Ti_(0.5),Zr_(0.5))O₄ andCa₃(Ti_(0.5, Zr) _(0.5))₂O₇ are laminated by turns will be explained inthis example 17. The case on the silicon substrate and the case on plus1% strained Si substrate will be explained as this example. It waspossible to make the MOSFET which has the characteristic that thepermittivity is large, the leak current is small and the mobility islarge.

FIG. 34 is a sectional view of the gate insulating-film portion ofMOSFET of the example of the invention. Since the structure was the sameeven if the strain of the substrate changed, the case of the siliconsubstrate and the plus 1% strained Si substrate was expressedcollectively.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the (001) Si substrate or thestrained Si substrate 171. And the gate electrode 173 is providedthrough the gate insulating film 172 on the channel region formedbetween these regions. The gate insulating film is a thin film whichlaminated by turns the Ruddlesden-Popper (RP) type structure which isformed in the form where a CaO layer touches a silicon substrate, and isexpressed with Ca₂(Ti_(0.5), Zr_(0.5))O₄ and Ca₃(Ti_(0.5),Zr_(0.5))₂O₇.

The thickness of the perovskite portion is one layer or two layers, andthe index of RP type structure is 1 or 2. That is, it is the mutuallamination thin film of RP1 type and RP2 type. The method mentionedabove about the example 9 was used for the manufacturing method of thestrained Si substrate. And the amount of strain at this time was plus1%. Also in subsequent examples, the strained Si substrate which has +1%of this amount of strain will be used. Hereafter, a film forming processis explained briefly.

First, the CaO layer was grown epitaxially on the (001) Si substrate andthe strained Si substrate using MBE. The surface of the Si substrate andthe surface of the strained Si substrate were Hydrogen-terminated by HFprocessing and NH₄F, and CaO was formed as a film after an appropriatetime. Although the planarizing of the substrate included manyprocessing, the planarizing of the substrate used here was processing toa grade in which atomic steps did not appear in all over the gateinsulating film. Since the region of the gate insulating film isbecoming small now, the present processing method may be enough forplanarizing processing.

The CaO thin film was grown for 2 ML under the environment where thereis no ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was200 degrees centigrade, and the ozone flux 1.5×10¹² molecule/second cm²was irradiated to the film for 30 seconds under the environment wherethe pressure was 10⁻⁶ Pa and the substrate temperature was 200 degreescentigrade. Thereby, two layers of CaO layers are made. After growingthe metal (Ti, Zr) for 1 ML on it so that Ti:Zr=0.5:0.5, the same ozoneflux as the above was irradiated for 20 seconds. Then, the(Ti_(0.5),Zr_(0.5))O₂ film was grown for 1 ML.

Next, after growing the metal (Ti, Zr) for 2 ML on it so thatTi:Zr=0.5:0.5, the same ozone flux as the above was irradiated for 40seconds. Then, the (Ti_(0.5),Zr_(0.5))O₂ film was grown for 2 ML. And,the mutual lamination thin film of RP1 type and RP2 type grewepitaxially on the silicon substrate and the strained Si substrate byrepeating this process.

Thus, finally the Ca₂(Ti_(0.5),Zr_(0.5))O₄ thin film was grownepitaxially for 52 angstroms by real thickness.

It was a thin gate insulating film with the thickness converted intoSiO₂ thickness (EOT) of 4.5 angstroms, where the permittivity was about45. Moreover, the leak current when applying the big electric field of 5MV/cm was as small as 1.2×10⁻³ A/cm² on the strained Si substrate. Thisis because real thickness is as thick as 52 angstroms.

However, since it increased also to it, well structure was made byhaving laminated RP1+RP2 and by turns and the level inside a well wasleveled completely, it is large as an effect that the barrier forelectrons went up greatly. On the silicon substrate, the leak currentincreased to a twice value of 2.5×10⁻³ A/cm². This is because of thenoise accompanying the increase in an interface electric charge trap.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 8×10⁵ A/cm², and reached 6.7×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of the multi quantum well structure gate insulating filmlaminated by turns of RP1+RP2 was very large.

Next, the effect that the lattice constant of the gate 25 insulatingfilm was in agreement with the lattice constant of the substrate wasinvestigated.

The interface electric charge trap density Dit (cm⁻²/eV) of MOSFET madeon the strained Si substrate was quite low value of 2×10¹¹ cm² /eV.Although this value is larger than the latest best value of 10¹⁰cm²/eVat SiO₂/Si interface, it is a quite desirable value. The effect of thelattice constant of the gate insulating film being in agreement with thelattice constant of the substrate and using the strained Si substrateenables the mobility being 800 (cm²/Vsec) at the maximum. This value isthe desirable value acquired only when the lattice constant was shiftedfor only 0.5% to the lattice constant of the strained Si substrate.

On the other hand, the interface electric charge trap density Dit(cm⁻²/eV) of the MOSFET on the silicon substrate was 8×10¹¹ cm⁻²/eV.Since there was about 1.5% of deviation of the lattice constant, theinterface electric charge trap density Dit was somewhat large.Consequently, although the mobility doesn't rise for the strain sincethe Si substrate is used, the mobility is realized 400 (cm²/Vsec) at themaximum. This value can be called good value if it takes intoconsideration that the lattice constant has shifted from the latticeconstant of a silicon substrate about 1.5%. However, it was a still verydesirable value.

If the lattice constant of the gate insulating film can be made more inagreement with the lattice constant of the substrate even if on thesilicon substrate, the more desirable value of mobility is expectable.Since a discrete energy level is formed and the well structure is madein RP1+RP2 type structure, the barrier for electrons can be kept largeenough as long as this structure is maintained.

Therefore, what is necessary is to consider only a lattice constant. Asfor the thin film which laminated by turns RP type structure expressedwith Ca₂(Tio.₅,Zro.₅)0 ₄, Ca₃ (Ti_(0.5), Zr_(0.5))₂O₇, (Ca_(0.4),Sr_(0.6))₂TiO₄ and (Ca_(0.4),Sr_(0.6))₃Ti₂O₇ as examples, a latticeconstant is in agreement with a silicon substrate. Therefore, it waspossible to have created MOSFET (for the former two materials to be 505cm²/Vsec and for the latter two materials to be 455 cm²/Vsec) whichshows high mobility. Although the performance is falling [latter ones]about ten percent, since-the substance which constitutes an interface is(Ca0.4, Sr0.6)0, this is because roughness is made to the interfacecompared with the time of CaO. However, the effect of the difference ofa lattice constant is far more important, and as long as it makes thedemerit of (Ca0.4, Sr0.6)O being a mixed crystal completely like thecreation process of a CaO film, you may say that there is almostnothing.

If the lattice constant of the gate insulating film exceeds plus 1.5% ofthe substrate lattice constant, an interface electric charge trap willincrease rapidly to 10¹⁴ cm⁻²/eV at +2% of the lattice constant.Therefore, it is necessary to stop the lattice constant of the gateinsulating film by +1.5%. You may.think that this point is a request inthe case of creating the thin film of rocksalt structure on a siliconsubstrate or a strained Si substrate. If it is rocksalt structure, mixedcrystal films, such as (Ca0.4, Sr0.6)O, is also the same, and in orderto create a good interface, it is required for a lattice constantdifference with a substrate to be less than 1.5%.

Although it was here shown in the example on the strained Si substratethat Ca₂(Ti_(0.5),Zr_(0.5))O₄ and the lamination structure ofCa₃(Ti_(0.5),Zr_(0.5))₂O₇ are promising, it is Sr₂TiO₄ and Sr₃Ti₂O₇lamination structure etc. is promising. Since it is necessary especiallyas a B site to make temperature of K cell into high temperature in MBEgrowth to use Zr and Hf, the film forming of only Ti is easier. At themeaning, it is Sr₂TiO₄. And it can be said that the lamination structureof Sr₃Ti₂O₇ is more effective. This point is being able to say similarlyabout other examples. This means being so effective, if B site is thesubstance of only Ti even if strain is on a silicon substrate and thereis nothing, since it is concerned with the ease of MBE film forming.

The Eighteenth Example

Next, the MOSFET in which the material which is correspond to the regionA or the region B expressed in FIG. 35 is provided as the insulatingfilm will be explained as the eighteenth example of the presentinvention. FIG. 36 expresses the case where Hf is introduced. As aresult of creating MOSFET in parallel and comparing in the followingexample, there was almost no difference between the case of Zr and thecase of Hf.

In FIG. 35, the region A expresses the range of materials optimum in theepitaxial growth on the silicon substrate and the region B expresses therange of materials optimum in the epitaxial growth on the +1% strainedSi substrate. In this example 18, the case of Sr₃TiO₅ is explained as anexample of actual MOSFET structure. Hereafter, the case on the siliconsubstrate and the.case on plus 1% strained Si substrate are described asthis example. It was possible to make the MOSFET which has thecharacteristic that the permittivity is large, the leak current is smalland the mobility is large.

FIG. 37 is a sectional view of the gate insulating-film portion of theMOSFET of the example of the invention. Since the structure is the sameeven if the strain of the substrate changes, the case of siliconsubstrate or +1% strained Si substrate is expressed.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the (001) Si substrate or thestrained Si substrate 181. And the gate electrode 183 is providedthrough the gate insulating film 182 on the channel region formedbetween these regions. The gate insulating film is a thin film of the“in phase structure” expressed with Sr₃TiO₅, which the SrO layer isformed in the form which touches a silicon substrate. In “in phasestructure”, as mentioned above, when two layers of AO(s) are inserted,the B-O axis of the direction of thickness of ABO₃ will be in agreement.That is, the phase of ABO₃ is in agreement in the direction ofthickness. Moreover, since it expresses like IPn according to the numbern of layers of the perovskite type substance ABO₃, it will be called IPIstructure here. The method described in the example 9 is used for themanufacturing method of the strained Si substrate. And the amount ofstrain at this time was +1%. Also in subsequent examples, the strainedSi substrate which has +1% of this amount of strain will be used.Hereafter, a film forming process is explained briefly

First, the CaO layer was grown epitaxially on the (001) Si substrate andthe strained Si substrate using MBE. The surface of the Si substrate andthe surface of the strained Si substrate were Hydrogen-terminated by HFprocessing and NH₄F, and SrO was formed as a film after an appropriatetime. Although the planarizing of the substrate included manyprocessing, the planarizing of the substrate used here was processing toa grade in which atomic steps did not appear in all over the gateinsulating film. Since the region of the gate insulating film isbecoming small now, the present processing method may be enough forplanarizing processing.

The SrO thin film was grown for 3 ML under the environment where thereis no ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was200 degrees centigrade, and the ozone flux 1.5×10¹² molecule/second cm²was irradiated to the film for 45 seconds under the environment wherethe pressure was 10⁻⁶ Pa and the substrate temperature was 200 degreescentigrade.

Thereby, three layers of SrO layers were made. After growing the Timetal for 1 ML on it, the same ozone flux as the above was irradiatedfor 20 seconds. Then, TiO₂ film was grown for 1 ML. By repeating thisprocess, Sr₃TiO₅ thin film was grown epitaxially on the siliconsubstrate and the strained Si substrate.

Thus, finally the Sr₃TiO₅ thin film was grown epitaxially for 60angstroms by real thickness.

It was a thin gate insulating film with the thickness converted intoSiO₂ thickness (EOT) of 6.9 angstroms, where the permittivity was about34. Moreover, the leak current when applying a big electric field of 5MV/cm was as small as 5×10⁻⁶ A/cm² on the Si substrate. This is becausethe real thickness is as thick as 51 angstroms. However, since wellstructure was made by RP1 structure film and the level inside a well wasleveled completely, the influence that the barrier for electrons went upgreatly affects thickness is the largest. On the no-strained siliconsubstrate, the leak current increased not a little to the twice value of10⁻⁵ A/cm². This is because of the noise accompanying the increase in aninterface electric charge trap.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁵ A/cm², and reached 2×10¹⁰ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of the Sr₃TiO₅ insulating film was very large.

Next, the effect of the lattice constant of the gate insulating filmbeing in agreement with the lattice constant of the substrate wasinvestigated. The interface electric charge trap densities Dit (cm⁻²/eV)of MOSFET made on the strained Si substrate were a quite low value of10¹¹ cm⁻²/eV. Although this value is larger than the latest best valueof 10¹⁰ cm⁻²/eV at SiO₂/Si interface, it is a quite desirable value.

Consequently, as for the mobility, 500 (cm²/Vsec) was realized at themaximum. This value is the desirable value acquired since the latticeconstant was in agreement with the lattice constant of the strained Sisubstrate. On the other hand, the interface electric charge trap densityDit (cm⁻²/eV) of MOSFET on the no-strained silicon substrate was 4×10¹¹/cm⁻²/eV. Since there was about 1% of deviation of the lattice constant,the interface electric charge trap density Dit was somewhat large.However, it was a still very desirable value. The mobility also raisedby strain since the strain Si substrate was used, and the mobility of750 (cm²/Vsec) was realized at the maximum. This value can be called adesirable value if it takes into consideration that the lattice constanthas shifted from the lattice constant of the silicon substrate about 1%.

If the lattice constant of the gate insulating film can be made more inagreement with the lattice constant of the substrate even if on thesilicon substrate, the more desirable value of mobility is expectable.What is necessary to keep the barrier for electrons large enough is justto form for example, Ca₃(Ti_(0.7,Zr) _(0.3))O₅ thin film,Sr₃(Ti_(0.2),Zr_(0.8))O₅ thin film and (Ba_(0.6),Sr_(0.4))₃TiO₅ thinfilm in RP1 type structure, as shown in FIG. 26A and FIG. 26B. In thiscase, as for mobility, 850, 850 and 840 (cm²/Vsec) are realized at themaximum, respectively.

If the lattice constant of the gate insulating film exceeds plus 1.5% ofthe substrate lattice constant, the interface electric charge trap willincrease rapidly to 10¹⁵ cm⁻²/eV when the lattice constant is +2%.Therefore, it is necessary to keep the lattice constant of the gateinsulating film less than. plus 1.5%.

Also in IP n (n =2, 3, 4, . . . ) type gate insulating film, if thematerial in the optimum region is used, the improvement of the sameorder in the characteristic of the leak current as the above will beseen. For example, as for the maximum of the mobility, 850 to 700cm²/Vsec is obtained on the strained Si substrate, and 505 to 400 areobtained on the Si substrate. When the difference of the latticeconstant of the gate insulating film and the lattice constant of thesubstrate exceeds 1.5%,. the interface electric charge trap increasesrapidly to 10¹⁴ cm⁻²/eV at plus 2%, and the mobility decreases rapidlyto below 225 cm²/Vsec even on the strained Si substrate.

Furthermore, the case where the thickness of the barrier portion islarger can also be considered. As structure when the thickness of thebarrier portion is still larger, since well structure is realized, itbecomes a very ideal material group from a viewpoint of a barrier forelectrons. Therefore, it will be judged whether the mismatch of thelattice constant is fundamentally contained in less than plus-or-minus1.5% of the lattice constant of the substrate in this case.

Since an electron and a hole are confined in the inside of the well withwell structure, it becomes unnecessary for the thickness to be large. Itis ideal if the permittivity is larger than 20, however, it may beemployable if the permittivity is larger than 10. When the thickness ofa barrier increased, since the permittivity of the whole film was thedirection which becomes low, the problem was seemed, but about by ten,if permittivity is good, also when a barrier becomes to some extentthick, it can use it as an insulating film. Although all structurescould not be shown, trial production and consideration at the time ofmaking a barrier layer into three or more (it having been made to changevariously also about a well portion) layers further were also performed.Although permittivity actually fell somewhat, in the leakcharacteristic, the problem was not produced at all. The point is thatwhen a too thick barrier is made, a multi quantum well structure havinga small EOT may not be obtained.

The Nineteenth Example

Next, the MOSFET in which the material which is corresponds to theregion A or Region B expressed in FIG. 38 is provided as the insulatingfilm will be explained as the nineteenth example of the presentinvention. FIG. 39 expresses the case where Hf is introduced. As aresult of creating MOSFET in parallel and comparing in the followingexample, there was almost no difference between the case of Zr and thecase of Hf.

In FIG. 38, the region A expresses the range of materials optimum in theepitaxial growth on the silicon substrate and the region B expresses therange of materials optimum in the epitaxial growth on the +1% strainedSi substrate. As an example of actual MOSFET structure, the structurewhere Sr₇Ti₃O₁₃, i.e., Sr₃TiO₅ and Sr₄Ti₂O₈ are laminated by turns willbe explained in this example 19. The case on the silicon substrate andthe case on plus 1% strained Si substrate will be explained as thisexample. It was possible to make the MOSFET which has the characteristicthat the permittivity is large, the leak current is small and themobility is large.

FIG. 40 is a sectional view of the gate insulating-film portion ofMOSFET of the example of the invention. Since the structure was the sameeven if the strain of the substrate changed, the case of the siliconsubstrate and the plus 1% strained Si substrate was expressedcollectively.

That is, in FET of this example, the source region S and the drainregion D are formed on the surface of the (001) Si substrate or thestrained Si substrate 191. And the gate electrode 193 is provided.through the gate insulating film 192 on the channel region formedbetween these regions. The gate insulating film is formed in the formwhere the SrO layer touches the silicon substrate, and is a thin film inwhich the In-Phase (IP) structure expressed with Sr₃TiO₅ and Sr₄Ti₂O₈ islaminated by turns.

The thickness of a perovskite portion is one layer or two layers, andthe index of IP type structure is 1 or 2. That is, it is the mutuallamination thin film of IP1 type and IP2 type. The method described inthe example 9 is adopted as a manufacturing method of the strained Sisubstrate. And the amount of the strain at this time was +1%. Also insubsequent examples, the strained Si substrate which has +1% of thisamount of strain will be used. Hereafter, a film forming process isexplained briefly.

First, the SrO layer was grown epitaxially on the (001) Si substrate andthe strained Si substrate using MBE. The surface of the Si substrate.and the surface of the strained Si substrate were Hydrogen-terminated byHF processing and NH₄F, and SrO was formed as a film after anappropriate time. Although the planarizing of the substrate includedmany processing, the planarizing of the substrate used here wasprocessing to a grade in which atomic steps did not appear in all overthe gate insulating film. Since the region of the gate insulating filmis becoming small now, the present processing method may be enough forplanarizing processing.

The SrO thin film was grown for 3 ML under the environment where thereis no ozone, the pressure was 10⁻⁷ Pa and the substrate temperature was200 degrees centigrade, and the ozone flux 1.5×10¹² molecule/second cm²was irradiated to the film for 45 seconds under the environment wherethe pressure was 10⁻⁶ Pa and the substrate temperature was 200 degreescentigrade. Then, SrO film was grown for 3 ML. After growing Ti metalfor 1 ML, the same ozone flux as the above was irradiated for 20seconds. Then, TiO₂ film was grown for 1 ML.

Next, after growing the SrO layer for 3 ML, Ti metal was grown for 2 MLand the same ozone flux as the above was irradiated for 40 seconds.Thereby, TiO₂ film was grown for 2 ML. By repeating this process, thethin film.laminated by IP1 type and IP2 type was grown epitaxially onthe silicon substrate and the strained Si substrate.

Thus, finally the Sr₇Ti₃O₁₃ thin film was grown epitaxially for 94angstroms by real thickness. It was a thin gate insulating film with thethickness converted into SiO₂ thickness (EOT) of 6.8 angstroms, wherethe permittivity was about 54. Moreover, the leak current when applyinga big electric field of 5 MV/cm was as small as 5×10⁻⁶ A/cm². This isbecause the real thickness is as thick as 94 angstroms. However, sinceit increased also to it, well structure was made by having laminatedIP1+IP2 and by turns and the semi-grade inside a well was leveledcompletely, it is large as an effect that the barrier for electrons wentup greatly. On the no-strained silicon substrate, the leak currentincreased not a little to the twice value of 10⁻⁵ A/cm². This is becauseof the noise accompanying the increase in an interface electric chargetrap.

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 10⁵ A/cm², and reached 2×10¹⁰ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of the multi quantum well structure gate insulating filmlaminated by turns of IP1+IP2 was very large.

Next, the effect of the lattice constant of the gate insulating filmbeing in agreement with the lattice constant of the substrate wasinvestigated. The interface electric charge trap densities Dit (cm⁻²/eV)of MOSFET made on the strained Si substrate were a quite low value of1.5×10¹¹ cm⁻²/eV. Although this value is larger than the latest bestvalue of 10¹⁰ cm⁻²/eV at SiO₂/Si interface, it is a quite desirablevalue.

The effect of the lattice constant of the gate insulating film being inagreement with the lattice constant of the substrate and using thestrained Si substrate enables the mobility being 825 (cm²/Vsec) at themaximum. This value is the desirable value acquired since the latticeconstant shifted for only 0.25% to the lattice constant of the strainedSi substrate.

On the other hand, the interface electric charge trap density Dit(cm⁻²/eV) of MOSFET on the no-strained silicon substrate was 3×10¹¹/cm⁻²/eV. Since there was about 0.75% of deviation of the latticeconstant, the interface electric charge trap density Dit was somewhatlarge. However, it was a still very desirable value. Although themobility didn't rise by strain since Si substrate was used, the mobilityof 455 (cm²/Vsec) was realized at the maximum. This value can be calleda desirable value if it takes into consideration that the latticeconstant has shifted from the lattice constant of the silicon substrateabout 0.75%.

If the lattice constant of the gate insulating film can be made more inagreement with the lattice constant of the substrate even if on thesilicon substrate, the more desirable value of mobility is expectable.With IP1+IP2 type structure, a discrete energy level is formed and thewell structure is made. Therefore, the barrier for electrons can be keptlarge enough as lonq.as this structure is maintained. Therefore, in thethin film which laminated by turns IP type structure expressed with(Sr_(0.2), Ca_(0.8))₃TiO₅ and (Sr_(0.2),Ca_(0.8))₄Ti₂O₈ that what isnecessary is to pay its attention only to a lattice constant, since alattice constant was in agreement with a silicon substrate, it waspossible to have created MOSFET (501 cm²/Vsec) which shows highmobility.

If the lattice constant of the gate insulating film exceeds +1.5% of thesubstrate lattice constant, the interface electric charge trap willincrease rapidly to 10¹⁴ cm⁻²/eV at plus 2% of the lattice constant.Therefore, it is necessary to keep the lattice constant of the gateinsulating film less than +1.5%. You may think that this point is arequest in the case of making the thin film of rocksalt structure on thesilicon substrate or the strained Si substrate. If it is rocksaltstructure, mixed crystal films, such as (Ca_(0.8),Sr_(0.2))O, are alsothe same, and in order to make a good interface, it is required for thedifference of the lattice constant with the substrate to be less than1.5%.

Although it was here shown in the example on the strained Si substratethat the lamination structure of Sr₃TiO₅ and Sr₄Ti₂O₈ is promising,other lamination structures , e.g., a lamination structure ofCa₃(Ti_(0.5),Zr_(0.5))O₅ and Ca₄(Ti_(0.5),Zr_(0.5))₂O₈, are promising.

The Twentieth Example

Next, the MIM capacitor in which the insulating film which has theIP1+IP2 type quantum well structure of SRO electrode/(IP1+IP2) thinfilm/SRO electrode is provided will be explained as the twentiethexample of the invention. FIG. 41 is a sectional view of the MIMcapacitor of this example. That is, this figure expresses a sectionalview of the MIM capacitor in which the quantum well is provided in itsinsulating-film. IP1+IP2 constitute the insulator film especially. Whenthe high dielectric constant film or the ferroelectric material film isused for the insulating-film portion and an MIM capacitor is constitutedfrom each case, dielectric property is good, and moreover leaks and anMIM capacitor with small current can be constituted. Here, SrRuO3 isused as the electrode.

Hereafter, this MIM: capacitor is explained according to themanufacturing process.

The capacitor was grown epitaxially on the (001) Si substrate 101 usingMBE. That is, SrTiO₃ layer 146 was grown epitaxially on the Si by thesame method as the tenth example.

Moreover, the SrRuO₃ electrode 143 was grown epitaxially, and the(Ba_(0.6),Sr_(0.4))O(001) layer was grown epitaxially on the SrRuO₃electrode 143. The thickness of (Ba, Sr)O layers was made into about 5.4angstroms.

The (Ba_(0.6),Sr_(0.4))TiO₃(001) layers was grown epitaxially for 3.95angstroms on the (Ba_(0.6),Sr_(0.4))O(001) layer. Furthermore,(Ba_(0.6),Sr_(0.4))O(001) film was grown epitaxially for the samethickness of 5.4 angstroms as the above on the (Ba, Sr)TiO₃ film.Furthermore, the (Ba_(0.6),Sr_(0.4))TiO₃ (001) layers 107 was grownepitaxially for 7.9 angstroms on the (Ba_(0.6),Sr_(0.4))O(001) film.Furthermore, the (Ba_(0.6),Sr_(0.4))O(001) film was grown epitaxiallyfor the same thickness of 5.4 angstroms as the above on the (Ba,Sr) TiO₃layers. This process of forming was repeated further three times(dielectric film 144), and the SrRuO₃ electrode 145 was grownepitaxially on it. At this time, all the thickness of the dielectric 144was 74 angstroms.

The condition of forming the capacitor was made that the pressure was10⁻⁶ Pa, the substrate temperature was 600 degrees centigrade, and theozone flux is 1.5×10¹² molecule /second cm².

Thus, the obtained insulating film was a capacitor with the thinthickness of 4.98 angstroms converted into SiO₂ thickness (EOT).Moreover, the leak current when applying the big electric field of 5MV/cm was as small as 2×10⁻⁴ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 5×10⁵ A/cm², and reached 2.5×10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Furthermore, the case where the ferroelectric film is used as adielectric film of this example is explained as a modification of thisexample. The SrRuO₃ electrode 143 was grown epitaxially and the. BaO(001) layer was grown epitaxially on the SrRuO₃ electrode 143 as theabove. The thickness of the BaO layer was made into about 5.5 angstroms.

The BaTiO₃ (001) layer was grown epitaxially for 4 angstroms on the BaOlayer. Furthermore, BaO (001) film was grown epitaxially for the samethickness of 5.5 angstroms as the above on the BaTiO₃ film. Furthermore,the BaTiO₃ (001) layer 107 was grown epitaxially for 8 angstroms on theBaO layer. Furthermore, BaO (001) film was grown epitaxially for thesame thickness of 5.5 angstroms as the above on the BaTiO₃ film. Thisprocess of forming was repeated further three times (dielectric film144), and the SrRuO₃ electrode 145 was grown epitaxially on it. At thistime, all the thickness of the dielectric 144 was 75.5 angstroms. Theinsulating film was a capacitor with the thin thickness of 5.9 angstromsconverted. into SiO₂ thickness (EOT). Moreover, the leak current whenapplying the big electric field of 5 MV/cm was as small as 4×10⁻⁵ A/cm².As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 2×10⁶ A/cm2, and reached 5×10⁹ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film ofMIM capacitor was very large.

Moreover, in this MIM capacitor, it turned out that the polarizationoccurred and the MIM structure of a ferroelectric thin film was made.Since the axis of the direction of thickness of each dielectric layerwas assembled, the characteristic as a ferroelectric material was alsovery large, and it turned out that the size of intrinsic polarizationhas the very large value which also reaches 48 micro C/cm². The value ofleak current is also very small, and since spontaneous polarization isvery large, it is very promising as aferroelectric-random-access-memory-oriented MIM capacitor.

The Twenty First Example

The MOSFET (MOS type field effect transistor) in which the insulatingfilm which has the double quantum well structure with buffer layer,i.e., CeO₂ (buffer layer)/ SrO/CeO₂/SrO/CeO₂/SrO, is provided will beexplained as the twenty-first example of the present invention.

FIG. 42 is a sectional view of the gate insulating-film of MOSFET of thetwenty-first example of the invention. That is, in FET of this example,the source region S and the drain region D are formed on the surface ofthe (001) Si substrate or the strained Si substrate 201. And the gateelectrode 208 is provided through the buffer layer 209 and the gateinsulating film 202 on the channel region formed between these regions.The gate insulating film has the double quantum well structure where theSrO barrier layer 203, the CeO₂ well layer 204, the SrO barrier layer205, the CeO₂ well layer 206, and the SrO barrier layer.207 were made tolaminate.

Hereafter, this insulating film 202 is explained in more detail alongwith that manufacture procedure.

That is, the (111) Si substrate 201 was Hydrogen-terminated by HFprocessing and NH₄F, and CeO₂ was formed as a film after an appropriatetime. Here, if it restricts when the flat nature of Si substrate is bad,it is also possible to put in epitaxial growth of Si regardless of aplane direction in the first step of a process. It is possible for thisto obtain Si substrate which overly has a flat side. Buffer CeO₂ (111)layer 209 was grown epitaxially thick for 14.1 angstroms. The conditionof forming the portion of capacitor was made that the pressure was 10⁻⁶Pa, the substrate temperature was 700 degrees, and the ozone flux is8.8×10¹² molecule/second cm².

The SrO (111) layer 203 was grown epitaxially. The thickness of the SrOlayer was made into about 5 angstroms. The condition of forming was madethat the pressure was 10⁻⁶ Pa, the substrate temperature was 700 degreescentigrade, and the ozone flux is 1.2×10¹² molecule/ second cm².

Next, the CeO₂ (111) layers 204 was grown epitaxially for 4.7 angstromson the SrO film. The condition of forming the capacitor was made thatthe pressure was 10⁻⁶ Pa, the substrate temperature was 700 degreescentigrade, and the ozone flux is 8.8×10¹² molecule/second cm².

Furthermore, the SrO (111) films 205 was grown epitaxially for 5angstroms on the CeO2. film under the environment that. the pressure was10⁻⁶ Pa, the substrate temperature was 700 degrees centigrade, and theozone flux was 1.2×10¹² molecule/second cm². Then, CeO₂ was grownepitaxially for only 9.4 angstroms. and SrO film was grown epitaxiallyfor 5 angstroms under the same environment as the above. And gold (Au)was formed as a film by vapor deposition on it as the gate electrode208.

Thus, the obtained insulating film 202 was an insulating film with thethin thickness converted into SiO₂ thickness (EOT) of 8.1 angstroms.Moreover, the leak current when applying the electric field of 5 MV/cmwas as small as 5×10⁻⁶ A/cm².

As a comparative example, the leak current of the insulating film whichconsists only of SiO₂ film in the same EOT when 5 MV/cm is applied byextrapolation is 1×10³ A/cm², and reached 2×10⁸ times of that of theabove-mentioned insulating film. From this, it has checked that theeffect of having made quantum well structure in the insulating film wasvery large even if the buffer layer existed. When that CeO₂ buffer layeris used, it is surmised that EOT increases about 1 angstrom. If it isthis EOT, it must be leak current which originally cuts 10⁻⁶ A/cm², butit seems that the leak current corresponding to 7A reduced by about 1Aas EOT in fact is flowing. However, it has still proved that the welltype insulating-film structure was effective.

Next, it was investigated in detail about the interface. In the casewhere the CeO₂ buffer layer was used, the interface level density bystrain of an interface has been reduced figures double or more than inthe case where it was laminated from SrO. Although CeO2 of a barrier (asopposed to an electron at an interface with Si) is low, the latticeconstant difference with Si is small. Since the difference of thelattice constant is small, it becomes easy not only to grow epitaxiallyon Si, but also to reduce the fall of the mobility of the transistor byan interface level. Moreover, since the permittivity of CeO₂ is verylarge, the buffer layer portion hardly affects the potential drop.Therefore, since the first layer was constituted thickly, the wholeinsulating film was improved very much. This point has to be noted.

Heretofore, embodiments of the invention have been explained in detailwith reference to some specific examples. The invention, however, is notlimited to these specific examples.

While the present invention has been disclosed in terms of theembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. An insulating film comprising: a first barrier layer consisting of amaterial having a first bandgap and a first relative permittivity; awell layer provided on the first barrier layer, consisting of a materialhaving a second bandgap smaller than the first bandgap and having asecond relative permittivity larger than first relative permittivity,discrete energy levels being formed in the well layer by a quantumeffect; and a second barrier layer provided on the well layer,consisting of a material having a third bandgap larger than the secondbandgap and having a third relative permittivity smaller than secondrelative permittivity.